A Quick recap for those who can't be bothered drilling down through the reply tree to it's darkest depths. We have successfully compiled Glib by first renaming all the library files s/.lib/.a/i (here's a program), then appending the Glib libraries to EXTRALIBS and LDLOADLIBS in the Makefile. This is dispite Makefile.PL being given this information by CPAN and MakeMaker.
Hence for any required Glib|Gtk library file, $ENV{'GTK_BASEPATH'}.'\lib\'.$lib_file has to be appended to the end of LDLOADLIBS in the Makefile.