CMake: pkg-config: fix usage for RedHat-like systems (#728)
$prefix/lib isn't in pc_path on Fedora 28:
[root@fedora-28 ~]# pkg-config --variable=pc_path pkg-config
/usr/lib64/pkgconfig:/usr/share/pkgconfig
This has the effect that the pkg-config file is written to the
correct location but pkg-config --libs raylib doesn't output
the correct library path. This fixes this problem by substituting
the directory names into the .pc, same as we do with the CMakeLists.txt
since #518.
This issue popped up during the automated test of the Perl bindings:
https://github.com/athreef/Alien-raylib/issues/3
Ahmad Fatoum