Cygwin - make check broken

It looks like when we changed regress/GNUmakefile to pull rules from
Makefile.shlib, cygwin got broken in the process.

The problem is that regess.dll ends up being a symlink back to itself,
because we do a:
$(NAME)$(DLSUFFIX): $(shlib)
        rm -f $(NAME)$(DLSUFFIX)
        $(LN_S) $(shlib) $(NAME)$(DLSUFFIX)

And from Makefile.shlib (for cygwin)
ifeq ($(PORTNAME), cygwin)
  shlib                 = $(NAME)$(DLSUFFIX)

Thus regress.dll gets unhappy :-(

I don't know enough about the rest of the way the cygwin port is put
together, but it seems that the other platforms all have
shlib=lib$(NAME)...

	-rocco