Add entry for __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4, to better reflect the
entries of items in config.h.in.  We are not currently defining this here
as the pre-configured config.h.win32.in is primarily meant for Visual
Studio builds of GLib-the MinGW/GCC/Clang builds of GLib will normally
use the autotools builds, which should give the correct config.h entries
upon running ./configure.