cmake: append LIB_SUFFIX to LIBRARY_INSTALL_DIR

Some Linux distributives requires to install libraries in 'lib64' directory on many 64-bit platforms. I add LIB_SUFFIX to select 'lib' vs 'lib64'.

This patch is used in Fedora: http://pkgs.fedoraproject.org/cgit/gflags.git/plain/gflags-0001-cmake-append-LIB_SUFFIX-to-LIBRARY_INSTALL_DIR.patch