Fix libdir location in pkgconfig files.

[richmattes]

The pkgconfig files currently hardcode the library directory as ${prefix}/lib, but the library installation directory in config.mk is set as ${prefix}/lib${LIB_SUFFIX}. This causes a mismatch between the library installation directory and the pkgconfig file on redhat-based 64-bit systems.

This commit remedies the issue for both the Makefile and CMake build by modifying the pkgconfig files to use CMAKE_INSTALL_LIBDIR instead of lib. In the CMake system, this directly reflects the installation path. The Makefiles were modified to replace CMAKE_INSTALL_LIBDIR with lib${LIB_SUFFIX}, matching the libdir definition in config.mk and following the pattern used in defining the prefix.

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[richmattes]

This should also address #2990.