Use the same name as glibc & gnulib to indicate "newlib itself is
being compiled". This also harmonizes the codebase a bit in that
_LIBC was already used in places instead of _COMPILING_NEWLIB.
Building for bfin-elf, mips-elf, and x86_64-pc-cygwin produces
the same object code.
This code looks like it's written to be copied & pasted between diff
C libraries and relies on _LIBC only being used with glibc. This will
break when newlib changes from _COMPILING_NEWLIB to _LIBC, so delete
the glibc-specific logic ahead of time.
Mike Frysinger
Steve Ellcey