Rename diagnostic-spec.{cc,h} to gcc-diagnostic-spec.{cc,h}

Rename diagnostic-spec.{cc,h} to gcc-diagnostic-spec.{cc,h}

This has GCC-specific stuff in it (options and "GTY"), and so should
not be in the "diagnostics/" subdir, and should avoid a "diagnostics"
prefix in its name.

No functional change intended.

gcc/ChangeLog:
	* Makefile.in (OBJS-libcommon): Replace diagnostic-spec.o with
	gcc-diagnostic-spec.o.
	(GTFILES): Replace diagnostic-spec.h with gcc-diagnostic-spec.h.
	* diagnostic-spec.cc: Move to...
	* gcc-diagnostic-spec.cc: ...here.
	* diagnostic-spec.h: Move to...
	* gcc-diagnostic-spec.h: ...here.
	* gengtype.cc (open_base_files): Replace diagnostic-spec.h with
	gcc-diagnostic-spec.h.
	* warning-control.cc: Likewise.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>