glib: Update snapshot version to 2.38.2

This is the latest stable release from upstream. Patches have been
refreshed, including putting the removal of most pkg-config checks into
the glib-only patch. A few more files, most notably the large NEWS file,
have also been removed from the repo to keep the size of the snapshot
down.
glib: Fix Makefiles to suppress warnings from automake

With the newly added glib.mk, some of the noinst_* variables need to use
+= in the evaluation to avoid multiple definition warnings from
automake.