Re: patch to common.make for cygwin paths

[Nicola Pero]

> I get the bogus warning when compiling on Windows and it really is 
> annoying/confusing. So it would be nice to fix it. I guess at the risk 
> of expanding the code infinitely, we could do:
> 
> ifeq ($(findstring mingw, $(GNUSTEP_TARGET_OS)), mingw)
>   ...windows specific check
> else
>   ...unix specific check
> endif
> 
> (also including cygwin)

Ok - I committed something of this kind - it didn't break unix :-) - let
me know if it fixes the spurious warning on windows or not.