* c-lex.c (map): Make const.
	(cb_file_change): Update for callback passing a line map.
	Don't assume we have a previous map.  Remove sanity check
	about popping too many files.
	* cpperror.c (print_location): Make map const.
	* cppfiles.c (stack_include_file): Update; line maps now hold sysp.
	(cpp_make_system_header): Similarly.
	(search_from): Similarly.
	(_cpp_execute_include): Don't remember where we came from.
	* cpphash.h (struct cpp_buffer): Remove return_to_line, sysp.
	(struct cpp_reader): Make map const.
	(CPP_IN_SYSTEM_HEADER, _cpp_do_file_change): Update.
	* cpplib.c (do_line): Update; line maps now hold sysp.
	(cpp_push_buffer): Similarly.
	(_cpp_do_file_change): Similarly; callback with map instead.
	(cpp_get_line_maps): Constify return value.
	(_cpp_pop_buffer): Update.
	* cpplib.h (struct cpp_file_change): Remove.
	(struct cpp_callbacks): Update.
	(cpp_get_line_maps): Constify return value.
	* cppmacro.c (_cpp_create_definition): Update.
	* cppmain.c (struct printer): Constify map.
	(maybe_print_line): Similarly.
	(print_line): Similarly.  Deduce flags 1 and 2 here.
	(cb_file_change): Update.
	* line-map.c (free_line_maps): Warn regardless.
	(add_line_map): Return pointer to const.  When passed NULL to_file
	with LC_LEAVE, use the obvious values for the return point so the
	caller doesn't have to figure them out.
	(lookup_line): Return pointer to const.
	(print_containing_files): Take pointer to const.
	* line-map.h (struct line_map): New members reason, sysp.
	(add_line_map): Return pointer to const.
	(lookup_line): Similarly.
	(print_containing_files): Take pointer to const.

From-SVN: r44789