c++: Module parsing

c++: Module parsing

This adds the module-declaration parsing and other logic.  We have two
new kinds of declaration -- module and import.  Plus the ability to
export other declarations.  The module processing can also divide the
TU into several portions -- GMF, Purview and PMF.

There are restrictions that some declarations must or mustnot appear
in a #include, so I needed to add a bit to indicate whether a token
came from the main source or not.  This seemed the least unpleasant
way of implementing such a check.

	gcc/cp/
	* parser.h (struct cp_token): Add main_source_p field.
	* parser.c (cp_lexer_new_main): Pass thought module token filter.
	Check macros.
	(cp_lexer_get_preprocessor_token): Set main_source_p.
	(enum module_parse): New.
	(cp_parser_diagnose_invalid_type_name): Deal with unrecognized
	module-directives.
	(cp_parser_skip_to_closing_parenthesize_1): Skip module-directivres.
	(cp_parser_skip_to_end_of_statement): Likewise.
	(cp_parser_skiup_to_end_of_block_or_statement): Likewise.
	(cp_parser_translation_unit): Add module parsing calls.
	(cp_parser_module_name, cp_parser_module_declaration): New.
	(cp_parser_import_declaration, cp_parser_module_export): New.
	(cp_parser_declaration): Add module export detection.
	(cp_parser_template_declaration): Adjust 'export' error message.
	(cp_parser_function_definition_after_declarator): Add
	module-specific logic.
	* module.cc (import_module, declare_module)
	(maybe_check_all_macros): Stubs.