c++: Final module preparations

c++: Final module preparations

This adds the final few preparations to drop modules in.  I'd missed a
couple of changes to core compiler -- a new pair of preprocessor
options, and marking the boundary of fixed and lazy global trees.

For C++, we need to add module.cc to the GTY scanner.  Parsing final
cleanups needs a few tweaks for modules.  Lambdas used to initialize a
global (for instance) get an extra scope, but we now need to point
that object to the lambda too.  Finally template instantiation needs
to do lazy loading before looking at the available instantiations and
specializations.

	gcc/
	* gcc.c (cpp_unique_options): Add Mmodules, Mno-modules.
	* tree-core.h (enum tree_index): Add TI_MODULE_HWM.
	gcc/cp/
	* config-lang.in (gtfiles): Add cp/module.cc.
	* decl2.c (c_parse_final_cleanups): Add module support.
	* lambda.c (record_lambda_scope): Call maybe_attach_decl.
	* module.cc (maybe_attach_decl, lazy_load_specializations): Stubs.
	(finish_module_procesing): Stub.
	* pt.c (lookup_template_class_1): Lazy load specializations.
	(instantiate_template_1): Likewise.