Fix implicit extern "C" breakage introduced by tokenization patch.

Fix implicit extern "C" breakage introduced by tokenization patch.

	* cp/parser.c (struct cp_token): new one-bit field , implicit_extern_c
	(cp_lexer_get_preprocessor_token): Set implicit_extern_c for
	tokens that come from headers that are implicitly extern "C".
	(struct cp_parser): new one-bit field, implicit_extern_c.
	(cp_parser_new): Set parser's implicit_extern_c to false.
	(cp_parser_translation_unit): Pop lang context if we were in a
	header that was implicitly extern "C".
	(cp_parser_declaration_seq_opt): Push/pop lang context as
	required by the token's and parser's implicit_extern_c.

From-SVN: r88203