Fix pkgconfig libdir paths.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -336,7 +336,7 @@
 set(VERSION "${PROJECT_VERSION}")
 set(prefix "${CMAKE_INSTALL_PREFIX}")
 set(exec_prefix "\${prefix}")
-set(libdir "\${exec_prefix}/lib")
+set(libdir "${LIB_INSTALL_DIR}")
 set(includedir "\${prefix}/include")
 set(PTHREAD_LIBS "${CMAKE_THREAD_LIBS_INIT}")
 
--- a/libical.pc.in
+++ b/libical.pc.in
@@ -8,7 +8,7 @@
 Name: libical
 Description: An implementation of basic iCAL protocols
 Version: @LIBICAL_LIB_VERSION_STRING@
-Libs: -L${libdir} -lical -licalss -licalvcal
+Libs: -lical -licalss -licalvcal
 Libs.private: @PTHREAD_LIBS@
 @REQUIRES_PRIVATE_ICU@
 Cflags: -I${includedir}
--- a/src/libical-glib/CMakeLists.txt
+++ b/src/libical-glib/CMakeLists.txt
@@ -233,7 +233,7 @@
 
 set(prefix "${CMAKE_INSTALL_PREFIX}")
 set(exec_prefix "\${prefix}")
-set(libdir "\${exec_prefix}/lib")
+set(libdir "${LIB_INSTALL_DIR}")
 set(includedir "\${prefix}/include")
 
 configure_file(
--- a/src/libical-glib/libical-glib.pc.in
+++ b/src/libical-glib/libical-glib.pc.in
@@ -8,4 +8,4 @@
 Version: @LIBICAL_LIB_VERSION_STRING@
 Requires: glib-2.0, gobject-2.0, libical
 Cflags: -I${includedir}
-Libs: -L${libdir} -lical-glib
+Libs: -lical-glib