re PR driver/20425 (-print-search-dirs doesn't honor mutil-os/multilib settings)

re PR driver/20425 (-print-search-dirs doesn't honor mutil-os/multilib settings)

	PR driver/20425
	* gcc.c (for_each_path): New function.
	(add_to_obstack, file_at_path): New functions.
	(struct file_at_path_info, struct add_to_obstack_info): New.
	(build_search_list): Rewrite using for_each_path.  Constify struct
	path_prefix pointer.  Add do_multi param.  Adjust all callers.
	(find_a_file): Similarly, but just change existing param to bool.
	(putenv_from_prefixes): Add do_multi param, make "paths" const.
	(do_spec_path): Delete.
	(struct spec_path_info): New.
	(spec_path): New function.
	(do_spec_1): Use for_each_path for %D and %I.
	(find_file): Adjust for find_a_file changes.
	(main): Search multilibs for specs.  Print multilib lib path for
	-print-search-dirs.  Likewise add multilibs to LIBRARY_PATH_ENV.
	(read_specs): Search multilibs for %include and %include_noerr.
	(is_directory): Remove second string param.  Change last param
	to a bool.  Don't use concat.  Remove SMALL_ARG_MAX test, always
	check path is a dir.  Update all callers.
	* doc/hostconfig.texi (SMALL_ARG_MAX): Remove mention.
	* system.h (SMALL_ARG_MAX): Poison.
	* config.gcc: Don't define SMALL_ARG_MAX.
	* config.host: Likewise.
	* config.build: Likewise.

From-SVN: r108635