* config/darwin-c.c (add_framework): Copy the directory name as it
	can be freed later.  Also, ensure we always allocate enough room
	for the cached framework information.
	(find_subframework_header): Keep track of the directory where the
	subframework header was found.
	(framework_construct_pathname): Speed up by not trying to re-add a
	framework.
	* cppfiles.c (search_path_exhausted): Arrange for the missing
	header callback to be able to set the directory where the header
	was found.
	(cpp_get_dir): Add.
	* cpplib.h (missing_header_cb): Add a parameter.
	(cpp_get_dir): Add.

From-SVN: r81534