Target CPU/OS/OBJFMT identifiers

[Iain Buclaw]

One small addition from GDC is the emitting of version identifiers related to
target cpu arch/tune set on the compiler.

For example, on i386, compile with -msse and version(GNU_MMX) and (GNU_SSE) will be
emitted to the frontend. Doing this requires C target objs linked in, which can
pull some unwanted dependencies from the GCC C compiler (as some MinGW users are
finding out).

Just out of curiosity, would anyone miss this extraneous feature if it were to be
pulled out?

Regards