langhooks: preprocessor hooks for c++ modules

langhooks: preprocessor hooks for c++ modules

This is a slightly modified version of 01-langhooks.def.  I realized I
didn't need the deferred macro langhook -- that can be directly
installed into the preprocessor callbacks via preprocess_options lang
hook.

	gcc/
	* langhooks-def.h (LANG_HOOKS_PREPROCESS_MAIN_FILE)
	(LANG_HOOKS_PREPROCESS_OPTIONS, LANG_HOOKS_PREPROCESS_UNDEF)
	(LANG_HOOKS_PREPROCESS_TOKEN): New.
	(LANG_HOOKS_INITIALIZER): Add them.
	* langhooks.h (struct lang_hooks): Add preprocess_main_file,
	preprocess_options, preprocess_undef, preprocess_token hooks.  Add
	enum PT_flags.
	gcc/c-family/
	* c-lex.c: #include "langhooks.h".
	(cb_undef): Maybe call preprocess_undef lang hook.
	* c-opts.c (c_common_post_options): Maybe call preprocess_options
	lang hook.
	(push_command_line_include): Maybe call preprocess_main_file lang
	hook.
	(cb_file_change): Likewise.
	* c-ppoutput.c: #include "langhooks.h.
	(scan_translation_unit): Maybe call preprocess_token lang hook.
	(class do_streamer): New, derive from token_streamer.
	(directives_only_cb): Data pointer is do_streamer, call
	preprocess_token lang hook.
	(scan_translation_unit_directives_only): Use do_streamer.
	(print_line_1): Move src_line recording to after string output.
	(cb_undef): Maybe call preprocess_undef lang hook.