Add --enable-build-with-cxx configure switch

This new option, disabled by default for now, allows specifying
whether to build GDB, GDBserver, and friends with a C++ (98/03)
compiler.

The name of the switch should be familiar to those who followed GCC's
own C++ conversion process.

. Adding -fpermissive to COMPILER in C++ mode (see the new
build-with-cxx.m4 file) makes errors like these be warnings instead:

  gdb/infrun.c:6597:1: error:   initializing argument 1 of ‘void sig_print_info(gdb_signal)’ [-fpermissive]
   sig_print_info (enum gdb_signal oursig)
   ^
  gdb/infrun.c: In function ‘void do_restore_infcall_suspend_state_cleanup(void*)’:
  gdb/infrun.c:7164:39: error: invalid conversion from ‘void*’ to ‘infcall_suspend_state*’ [-fpermissive]
     restore_infcall_suspend_state (state);
				 ^

so that the compiler carries on compiling the file.  -Werror still
catches the warnings, so nothing is lost, only our lifes are made
easier by concentrating on getting other more important things out of
the way first.

There's no way to quiet those warnings.  Until they're all fixed, when
building in C++ mode, -Werror is disabled by default.

. Adding -Wno-narrowing suppresses thousands of instances of this warning:

  gdb/arm-linux-tdep.c:439:1: error: narrowing conversion of ‘-1’ from ‘int’ to ‘ULONGEST {aka long unsigned int}’ inside { } is ill-formed in C++11 [-Werror=narrowing]
  gdb/arm-linux-tdep.c:439:1: error: narrowing conversion of ‘-1l’ from ‘LONGEST {aka long int}’ to ‘ULONGEST {aka long unsigned int}’ inside { } is ill-formed in C++11 [-Werror=narrowing]
  gdb/arm-linux-tdep.c:450:1: error: narrowing conversion of ‘-1’ from ‘int’ to ‘ULONGEST {aka long unsigned int}’ inside { } is ill-formed in C++11 [-Werror=narrowing]

We can defer handling those until we target C++11.


. Adding -Wno-sign-compare suppresses thousands of instances of this warning:

  gdb/linux-record.c:1763:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
	 if (tmpulongest == tdep->fcntl_F_GETLK64)
				  ^


. Adding -Wno-write-strings suppresses thousands of instances of this warning:

  gdb/mi/mi-cmd-var.c: In function ‘void mi_cmd_var_show_attributes(char*, char**, int)’:
  gdb/mi/mi-cmd-var.c:514:12: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
       attstr = "editable";
	      ^
  gdb/mi/mi-cmd-var.c:516:12: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
       attstr = "noneditable";
	      ^

For now, it's best to hide these warnings from view until we're
'-fpermissive'-clean, and can thus start building with -Werror.
The C compiler has always managed to build working GDBs with these
issues in the code, so a C++ compiler should too.

gdb/ChangeLog:
2015-02-27  Pedro Alves  <palves@redhat.com>

	* Makefile.in (COMPILER): New, get it from autoconf.
	(COMPILE.pre, CC_LD): Use COMPILER.
	(CXX): Get from autoconf instead.
	(CXX_FOR_TARGET): Default to g++ instead of gcc.
	* acinclude.m4: Include build-with-cxx.m4.
	* build-with-cxx.m4: New file.
	* configure.ac: Call AC_PROG_CXX and GDB_AC_BUILD_WITH_CXX.
	Disable -Werror by default if building in C++ mode.
	(build_warnings): Add -Wno-sign-compare, -Wno-write-strings and
	-Wno-narrowing in C++ mode.  Only enable -Wpointer-sign in C mode.
	Run supported-warning-flags tests with the C++ compiler.
	Save/restore CXXFLAGS too.
	* configure: Regenerate.

gdb/gdbserver/ChangeLog:
2015-02-27  Pedro Alves  <palves@redhat.com>

	* Makefile.in (COMPILER): New, get it from autoconf.
	(CXX): Get from autoconf instead.
	(COMPILE.pre): Use COMPILER.
	(CC-LD): Rename to ...
	(CC_LD): ... this.  Use COMPILER.
	(gdbserver$(EXEEXT), gdbreplay$(EXEEXT), $(IPA_LIB)): Adjust.
	(CXX_FOR_TARGET): Default to g++ instead of gcc.
	* acinclude.m4: Include build-with-cxx.m4.
	* configure.ac: Call AC_PROG_CXX and GDB_AC_BUILD_WITH_CXX.
	Disable -Werror by default if building in C++ mode.
	(build_warnings): Add -Wno-sign-compare, -Wno-write-strings and
	-Wno-narrowing in C++ mode. Run supported-warning-flags tests with
	the C++ compiler.  Save/restore CXXFLAGS too.
	* configure: Regenerate.

1 files changed, 374 insertions, 6 deletions

diff --git a/gdb/configure b/gdb/configure
index b1a766561b7..3297d37c5f0 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -724,6 +724,7 @@ MAKE
 CCDEPMODE
 DEPDIR
 am__leading_dot
+COMPILER
 INSTALL_STRIP_PROGRAM
 STRIP
 install_sh
@@ -742,6 +743,9 @@ build
 EGREP
 GREP
 CPP
+ac_ct_CXX
+CXXFLAGS
+CXX
 OBJEXT
 EXEEXT
 ac_ct_CC
@@ -796,6 +800,7 @@ enable_option_checking
 enable_maintainer_mode
 enable_plugins
 enable_largefile
+enable_build_with_cxx
 with_separate_debug_dir
 with_gdb_datadir
 with_relocated_sources
@@ -849,6 +854,9 @@ CFLAGS
 LDFLAGS
 LIBS
 CPPFLAGS
+CXX
+CXXFLAGS
+CCC
 CPP
 MAKEINFO
 MAKEINFOFLAGS
@@ -1484,6 +1492,7 @@ Optional Features:
 			  (and sometimes confusing) to the casual installer
   --enable-plugins        Enable support for plugins
   --disable-largefile     omit support for large files
+  --enable-build-with-cxx build with C++ compiler instead of C compiler
   --enable-targets=TARGETS
                           alternative target configurations
   --enable-64-bit-bfd     64-bit support (on hosts with narrower word sizes)
@@ -1567,6 +1576,8 @@ Some influential environment variables:
   LIBS        libraries to pass to the linker, e.g. -l<library>
   CPPFLAGS    C/C++/Objective C preprocessor flags, e.g. -I<include dir> if
               you have headers in a nonstandard directory <include dir>
+  CXX         C++ compiler command
+  CXXFLAGS    C++ compiler flags
   CPP         C preprocessor
   MAKEINFO    Parent configure detects if it is of sufficient version.
   MAKEINFOFLAGS
@@ -1696,6 +1707,44 @@ fi
 
 } # ac_fn_c_try_compile
 
+# ac_fn_cxx_try_compile LINENO
+# ----------------------------
+# Try to compile conftest.$ac_ext, and return whether this succeeded.
+ac_fn_cxx_try_compile ()
+{
+  as_lineno=${as_lineno-"$1"} as_lineno_stack=as_lineno_stack=$as_lineno_stack
+  rm -f conftest.$ac_objext
+  if { { ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:${as_lineno-$LINENO}: $ac_try_echo\""
+$as_echo "$ac_try_echo"; } >&5
+  (eval "$ac_compile") 2>conftest.err
+  ac_status=$?
+  if test -s conftest.err; then
+    grep -v '^ *+' conftest.err >conftest.er1
+    cat conftest.er1 >&5
+    mv -f conftest.er1 conftest.err
+  fi
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; } && {
+	 test -z "$ac_cxx_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then :
+  ac_retval=0
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	ac_retval=1
+fi
+  eval $as_lineno_stack; test "x$as_lineno_stack" = x && { as_lineno=; unset as_lineno;}
+  return $ac_retval
+
+} # ac_fn_cxx_try_compile
+
 # ac_fn_c_try_cpp LINENO
 # ----------------------
 # Try to preprocess conftest.$ac_ext, and return whether this succeeded.
@@ -3487,6 +3536,264 @@ ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
 ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
+ac_ext=cpp
+ac_cpp='$CXXCPP $CPPFLAGS'
+ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
+if test -z "$CXX"; then
+  if test -n "$CCC"; then
+    CXX=$CCC
+  else
+    if test -n "$ac_tool_prefix"; then
+  for ac_prog in g++ c++ gpp aCC CC cxx cc++ cl.exe FCC KCC RCC xlC_r xlC
+  do
+    # Extract the first word of "$ac_tool_prefix$ac_prog", so it can be a program name with args.
+set dummy $ac_tool_prefix$ac_prog; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if test "${ac_cv_prog_CXX+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$CXX"; then
+  ac_cv_prog_CXX="$CXX" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if { test -f "$as_dir/$ac_word$ac_exec_ext" && $as_test_x "$as_dir/$ac_word$ac_exec_ext"; }; then
+    ac_cv_prog_CXX="$ac_tool_prefix$ac_prog"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+CXX=$ac_cv_prog_CXX
+if test -n "$CXX"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $CXX" >&5
+$as_echo "$CXX" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+    test -n "$CXX" && break
+  done
+fi
+if test -z "$CXX"; then
+  ac_ct_CXX=$CXX
+  for ac_prog in g++ c++ gpp aCC CC cxx cc++ cl.exe FCC KCC RCC xlC_r xlC
+do
+  # Extract the first word of "$ac_prog", so it can be a program name with args.
+set dummy $ac_prog; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if test "${ac_cv_prog_ac_ct_CXX+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$ac_ct_CXX"; then
+  ac_cv_prog_ac_ct_CXX="$ac_ct_CXX" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if { test -f "$as_dir/$ac_word$ac_exec_ext" && $as_test_x "$as_dir/$ac_word$ac_exec_ext"; }; then
+    ac_cv_prog_ac_ct_CXX="$ac_prog"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+ac_ct_CXX=$ac_cv_prog_ac_ct_CXX
+if test -n "$ac_ct_CXX"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_ct_CXX" >&5
+$as_echo "$ac_ct_CXX" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+  test -n "$ac_ct_CXX" && break
+done
+
+  if test "x$ac_ct_CXX" = x; then
+    CXX="g++"
+  else
+    case $cross_compiling:$ac_tool_warned in
+yes:)
+{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: using cross tools not prefixed with host triplet" >&5
+$as_echo "$as_me: WARNING: using cross tools not prefixed with host triplet" >&2;}
+ac_tool_warned=yes ;;
+esac
+    CXX=$ac_ct_CXX
+  fi
+fi
+
+  fi
+fi
+# Provide some information about the compiler.
+$as_echo "$as_me:${as_lineno-$LINENO}: checking for C++ compiler version" >&5
+set X $ac_compile
+ac_compiler=$2
+for ac_option in --version -v -V -qversion; do
+  { { ac_try="$ac_compiler $ac_option >&5"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:${as_lineno-$LINENO}: $ac_try_echo\""
+$as_echo "$ac_try_echo"; } >&5
+  (eval "$ac_compiler $ac_option >&5") 2>conftest.err
+  ac_status=$?
+  if test -s conftest.err; then
+    sed '10a\
+... rest of stderr output deleted ...
+         10q' conftest.err >conftest.er1
+    cat conftest.er1 >&5
+    rm -f conftest.er1 conftest.err
+  fi
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }
+done
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether we are using the GNU C++ compiler" >&5
+$as_echo_n "checking whether we are using the GNU C++ compiler... " >&6; }
+if test "${ac_cv_cxx_compiler_gnu+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+#ifndef __GNUC__
+       choke me
+#endif
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  ac_compiler_gnu=yes
+else
+  ac_compiler_gnu=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_cv_cxx_compiler_gnu=$ac_compiler_gnu
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_cxx_compiler_gnu" >&5
+$as_echo "$ac_cv_cxx_compiler_gnu" >&6; }
+if test $ac_compiler_gnu = yes; then
+  GXX=yes
+else
+  GXX=
+fi
+ac_test_CXXFLAGS=${CXXFLAGS+set}
+ac_save_CXXFLAGS=$CXXFLAGS
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CXX accepts -g" >&5
+$as_echo_n "checking whether $CXX accepts -g... " >&6; }
+if test "${ac_cv_prog_cxx_g+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_save_cxx_werror_flag=$ac_cxx_werror_flag
+   ac_cxx_werror_flag=yes
+   ac_cv_prog_cxx_g=no
+   CXXFLAGS="-g"
+   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  ac_cv_prog_cxx_g=yes
+else
+  CXXFLAGS=""
+      cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+
+else
+  ac_cxx_werror_flag=$ac_save_cxx_werror_flag
+	 CXXFLAGS="-g"
+	 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  ac_cv_prog_cxx_g=yes
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+   ac_cxx_werror_flag=$ac_save_cxx_werror_flag
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_prog_cxx_g" >&5
+$as_echo "$ac_cv_prog_cxx_g" >&6; }
+if test "$ac_test_CXXFLAGS" = set; then
+  CXXFLAGS=$ac_save_CXXFLAGS
+elif test $ac_cv_prog_cxx_g = yes; then
+  if test "$GXX" = yes; then
+    CXXFLAGS="-g -O2"
+  else
+    CXXFLAGS="-g"
+  fi
+else
+  if test "$GXX" = yes; then
+    CXXFLAGS="-O2"
+  else
+    CXXFLAGS=
+  fi
+fi
+ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
+
 
 ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
@@ -4634,6 +4941,30 @@ ac_script='s/[\\$]/&&/g;s/;s,x,x,$//'
 program_transform_name=`$as_echo "$program_transform_name" | sed "$ac_script"`
 
 
+# See if we are building with C++, and substitute COMPILER.
+
+  # Check whether --enable-build-with-cxx was given.
+if test "${enable_build_with_cxx+set}" = set; then :
+  enableval=$enable_build_with_cxx; case $enableval in
+      yes | no)
+	  ;;
+      *)
+	  as_fn_error "bad value $enableval for --enable-build-with-cxx" "$LINENO" 5 ;;
+    esac
+else
+  enable_build_with_cxx=no
+fi
+
+
+  if test "$enable_build_with_cxx" = "yes"; then
+    # We're using -fpermissive as shortcut for now.
+    COMPILER='$(CXX) -fpermissive'
+   else
+    COMPILER='$(CC)'
+  fi
+
+
+
 # Dependency checking.
 rm -rf .tst 2>/dev/null
 mkdir .tst 2>/dev/null
@@ -13038,8 +13369,11 @@ if test "${enable_werror+set}" = set; then :
 fi
 
 
-# Enable -Werror by default when using gcc.  Turn it off for releases.
-if test "${GCC}" = yes -a -z "${ERROR_ON_WARNING}" && $development; then
+# Enable -Werror by default when using gcc in C mode.  Leave it off
+# for C++ until we're warning clean.  Turn it off for releases.
+if test "${GCC}" = yes -a -z "${ERROR_ON_WARNING}" \
+   && test x"$enable_build_with_cxx" != x"yes" \
+   && $development; then
     ERROR_ON_WARNING=yes
 fi
 
@@ -13048,13 +13382,21 @@ if test "${ERROR_ON_WARNING}" = yes ; then
     WERROR_CFLAGS="-Werror"
 fi
 
+# These options work in either C or C++ modes.
 build_warnings="-Wall -Wdeclaration-after-statement -Wpointer-arith \
--Wpointer-sign \
 -Wno-unused -Wunused-value -Wunused-function \
 -Wno-switch -Wno-char-subscripts -Wmissing-prototypes \
 -Wdeclaration-after-statement -Wempty-body -Wmissing-parameter-type \
 -Wold-style-declaration -Wold-style-definition"
 
+# Now add in C and C++ specific options, depending on mode.
+if test "$enable_build_with_cxx" = "yes"; then
+   build_warnings="$build_warnings -Wno-sign-compare -Wno-write-strings \
+-Wno-narrowing"
+else
+   build_warnings="$build_warnings -Wpointer-sign"
+fi
+
 # Enable -Wno-format by default when using gcc on mingw since many
 # GCC versions complain about %I64.
 case "${host}" in
@@ -13092,6 +13434,18 @@ if test x"$silent" != x"yes" && test x"$build_warnings" != x""; then
   echo "Setting GDB specific compiler warning flags = $build_warnings" 6>&1
 fi
 fi
+
+# The set of warnings supported by a C++ compiler is not the same as
+# of the C compiler.
+if test "$enable_build_with_cxx" = "yes"; then
+    ac_ext=cpp
+ac_cpp='$CXXCPP $CPPFLAGS'
+ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
+
+fi
+
 WARN_CFLAGS=""
 if test "x${build_warnings}" != x -a "x$GCC" = xyes
 then
@@ -13102,10 +13456,14 @@ $as_echo_n "checking compiler warning flags... " >&6; }
     for w in ${build_warnings}; do
 	case $w in
 	-Werr*) WERROR_CFLAGS=-Werror ;;
-	*) # Check that GCC accepts it
+	*)
+	    # Check whether GCC accepts it.
 	    saved_CFLAGS="$CFLAGS"
 	    CFLAGS="$CFLAGS $w"
-	    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+	    saved_CXXFLAGS="$CXXFLAGS"
+	    CXXFLAGS="$CXXFLAGS $w"
+
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
 int
@@ -13116,11 +13474,12 @@ main ()
   return 0;
 }
 _ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
+if ac_fn_cxx_try_compile "$LINENO"; then :
   WARN_CFLAGS="${WARN_CFLAGS} $w"
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	    CFLAGS="$saved_CFLAGS"
+	    CXXFLAGS="$saved_CXXFLAGS"
 	esac
     done
     { $as_echo "$as_me:${as_lineno-$LINENO}: result: ${WARN_CFLAGS} ${WERROR_CFLAGS}" >&5
@@ -13129,6 +13488,15 @@ fi
 
 
 
+if test "$enable_build_with_cxx" = "yes"; then
+   ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
+fi
+
 # In the Cygwin environment, we need some additional flags.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for cygwin" >&5
 $as_echo_n "checking for cygwin... " >&6; }