Reorganize pc files for a single library
After this commit, pc files no longer include the gdk backend in their name, and we no longer install a pc file for gdk. There is now a single gtk+-3.0.pc file. It turns out a separate gtk+-x11-3.0.pc file is not necessary, since gdkx.h doesn't have a separate include directory that would have to be added to Cflags.
Showing with 11 additions and 67 deletions