preprocessor: module line maps

preprocessor: module line maps

This patch adds LC_MODULE as a map kind, used to indicate a c++
module.  Unlike a regular source file, it only contains a single
location, and the source locations in that module are represented by
ordinary locations whose 'included_from' location is the module.

It also exposes some entry points that modules will use to create
blocks of line maps.

In the original posting, I'd missed the deletion of the
linemap_enter_macro from internal.h.  That's included here.

	libcpp/
	* include/line-map.h (enum lc_reason): Add LC_MODULE.
	(MAP_MODULE_P): New.
	(line_map_new_raw): Declare.
	(linemap_enter_macro): Move declaration from internal.h
	(linemap_module_loc, linemap_module_reparent)
	(linemap_module_restore): Declare.
	(linemap_lookup_macro_indec): Declare.
	* internal.h (linemap_enter_macro): Moved to line-map.h.
	* line-map.c (linemap_new_raw): New, broken out of ...
	(new_linemap): ... here.  Call it.
	(LAST_SOURCE_LINE_LOCATION): New.
	(liemap_module_loc, linemap_module_reparent)
	(linemap_module_restore): New.
	(linemap_lookup_macro_index): New, broken out of ...
	(linemap_macro_map_lookup): ... here.  Call it.
	(linemap_dump): Add module dump.