C++ Module options

C++ Module options

This adds the C++ module options, and wires them into lang-specs.  The
options are not connected to any machinery.  The options! They do
nothing!

	gcc/c-family/
	* c-opts.c (c_common_init_options): Ask for module dependencies.
	(c_common_handle_option): Handle -Mmodules -Mno-modules.
	* c-pch.c (c_common_valid_pch): ... does not play with C++
	modules.
	* c.opt (Mmodules, Mno-modules): New preprocessor dependency
	options.
	(fmodules-ts, fmodule-header, fmodule-implicit-inline)
	(fmodule-only, fmodule-mapper, fmodule-lazy)
	(fmodule-version-ignore, Winvalid-imported-macros)
	(flang-info-include-translate, flang-info-include-translate-not):
	New options
	gcc/cp/
	* lang-specs.h: Add module-related options.