win32: re-fix the _utf8 compat function situation

The previous fix didn't work, because every place within glib that
used any of the functions also needed to be including win32compat.h.

So, move the prototypes back to their original headers (but at least
all in one place at the bottom).

https://bugzilla.gnome.org/show_bug.cgi?id=688109

docs/reference/glib/Makefile.am

@@ -51,8 +51,7 @@ IGNORE_HFILES = \
 	gvariant-serialiser.h	\
 	gvariant-core.h		\
 	gvarianttypeinfo.h	\
-	gwakeup.h		\
-	gwin32compat.h
+	gwakeup.h
 
 # Images to copy into HTML directory
 HTML_IMAGES =  				\