configure.in: Prepend ${srcdir}/config/${cpu_type}/ instead of ${srcdir}/ginclude/ to every...
* configure.in: Prepend ${srcdir}/config/${cpu_type}/ instead of
${srcdir}/ginclude/ to every entry in extra_headers.
* configure: Regenerate.
* ginclude/math-3300.h: Rename to config/m68k/math-3300.h.
* ginclude/math-68881.h: Rename to config/m68k/math-68881.h.
* ginclude/ppc-asm.h: Rename to config/rs6000/ppc-asm.h.
* ginclude/proto.h: Rename to config/convex/proto.h.