need gcf dir with
  gcf/gcf.c
  gcf/gcf.h
  gcf/Makefile.PL

then

  $ mkdir PS-MOPS-GCR
  $ rsync gcf PS-MOPS-GCR
  $ h2xs -O -n PS::MOPS::GCR ./PS-MOPS-GCR/gcf/gcf.h
  # clean up PS-MOPS-GCR.xs
  # edit Makefile.PL
    MYEXTLIB => 'gcf/libgcf$(LIB_EXT)',

sub MY::postamble {
'
$(MYEXTLIB): gcf/Makefile
	cd gcf && $(MAKE) $(PASSTHRU)
';
}

