There's a bit of code in Makefile.PL (all but the top-level one) that tries to
add a conditional move to the end of each compilation step.  Currently it
looks like
  $inherited =~ s/CCCMD.*$/$&\n\t\@if test -f `basename \$*.o` -a 
"`basename \$*.o`" != "\$*.o"; then mv `basename \$*.o` \$*.o; fi/m;

but because of the new MakeMaker, really needs to be

  $inherited =~ s/CCCMD.*$/$&\n\t\@if test -f `basename \$*.o` -a 
"`basename\ $*.o`" != "\$*.o"; then mv `basename \$*.o` \$*.o; fi/mg;

(Note the added 'g' modifier.)

I have a patch file to do this, but don't see any place to attach it, and I 
don't think it'd survive inclusion in the description.  I'll be happy to mail it to 
anyone who desires it.  It's also available from

  http://www.headgear.org/~cloyce/Gtk-Perl-build.patch