[patch] Separate {OS,CPU}_CPP_BUILTINS macros into C-family and language-independent macros

[FX]

>>  -- alpha-dec-osf5.1 fails to build mips-tfile.o
> 
> I'll have a look, but the mips-tfile.o failure (known problem, cf. PR
> target/3746) shouldn't matter: mips-tfile is only used to introduce
> debug info into object files (not possible with the native as, and gas
> doesn't currently work on Tru64 UNIX).  Simpy build cc1 and test that.

OK, I've ignored the error and the build proceeded; it gives a working cc1, with correct built-in macros.

FX