corebase - configure and compiler checks

[Riccardo Mottola]

Hi,

I just modified CoreBase configure to use the compiler specified during 
make (if you do not decide to overrirde with CC). That way, if you have 
multiple compilers installed (e.g. gcc and clang, or several gcc 
versions) it will try to use the same or a mess happens. I suppose this 
should be good practice when mising configure with gnustep make, I will 
update other packages that way.

I noticed however that the existing configure file was checking 
explicitely for the objective-c preprocessor. GS make doesn't provide 
that value, I noticed it does not get used at all, so I removed it and 
everything worked fine. If instead it was of use, let's discuss an 
alternative solution. Perhaps a way do derive it from C or CPP ?

Riccardo