gmacros.h: Add Private Macro _GLIB_DEFINE_AUTOPTR_CHAINUP

gmacros.h: Add Private Macro _GLIB_DEFINE_AUTOPTR_CHAINUP

This is necessary as we are using _GLIB_AUTOPTR_TYPENAME and
_GLIB_AUTOPTR_FUNC_NAME in gtype.h for G_DECLARE_DERIVABLE_TYPE and
G_DECLARE_FINAL_TYPE, but _GLIB_AUTOPTR_TYPENAME and
_GLIB_AUTOPTR_FUNC_NAME expand to nothing on non-GCC, causing builds on
non-GCC to break, due to bad typedef and function definitions.

This patch defines a new private macro which does what is needed on GCC
builds and does nothing on non-GCC builds, thus fixing the build.

https://bugzilla.gnome.org/show_bug.cgi?id=743640