t-interix: Use mostly system headers unchanged.

t-interix: Use mostly system headers unchanged.

        * i386/t-interix: Use mostly system headers unchanged.
        Use system assert.h
        * fixinc/fixinc.interix: Ditto (make almost no-op).
        * config/x-interix.h (_ALL_SOURCE): add -D
        * config/x-interix.h (crti.o): Delete dependency.
        * config/xm-interix.h (ONLY_INT_FIELDS): Define only when bootstrapping.
        * i386/xm-i386-interix.h: New file.
        * i386/interix.h (ASM_OUTPUT_LIMITED_STRING): Fix warnings.
        * i386/i386-interix.h: Renamed from interix.h.
        * configure.in (interix): Use new files.
        * configure: Rebuilt.

From-SVN: r26332