Make pthreads linkage precise for the nowx build. Fixes issue 3875.
Fall back to pkg-config for gtk+-2.0 if cmake is version 2.8.2. That version has a bug that doesn't detect gdk-pixbuf-2.0.
git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@6810 8ced0084-cf51-0410-be5f-012b33b47a6e