diagnostics: move diagnostics_output_spec to diagnostics::output_spec

diagnostics: move diagnostics_output_spec to diagnostics::output_spec

No functional change intended.

gcc/ChangeLog:
	* Makefile.in (OBJS-libcommon): Replace diagnostic-output-spec.o
	with diagnostics/output-spec.o.
	* diagnostic-output-spec.cc: Move to...
	* diagnostics/output-spec.cc: ...here.  Update #include for
	move of diagnostic-output-spec.h to diagnostics/output-spec.h.
	(namespace::diagnostics_output_spec): Replace with...
	(namespace diagnostics::output_spec): ...this, removing redundant
	prefixes.
	(diagnostics_output_spec::gcc_spec_context): Replace with...
	(diagnostics::output_spec::dc_spec_context): ...this.
	(diagnostic_output_spec_cc_tests): Rename to...
	(diagnostics_output_spec_cc_tests): ...this.
	* diagnostic-output-spec.h: Move to...
	* diagnostics/output-spec.h: ...here and update inclusion guard.
	(namespace::diagnostics_output_spec): Replace with...
	(namespace diagnostics::output_spec): ...this, removing redundant
	prefixes.
	(diagnostics_output_spec::gcc_spec_context): Replace with...
	(diagnostics::output_spec::dc_spec_context): ...this.
	* libgdiagnostics.cc: Update #include for move of
	diagnostic-output-spec.h to diagnostics/output-spec.h.
	* opts-diagnostic.cc: Likewise.  Update for namespace and name
	changes.
	* selftest-run-tests.cc (selftest::run_tests): Update for renaming
	of diagnostic_output_spec_cc_tests to
	diagnostics_output_spec_cc_tests.
	* selftest.h (diagnostic_output_spec_cc_tests): Rename decl to...
	(diagnostics_output_spec_cc_tests): ...this.

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