* cppfiles.c (NO_INCLUDE_PATH): New macro.
	(find_include_file): Decide here which part of the include
	chain to start the search.  Complain about an empty include
	chain in all cases apart from an abolsute file name.
	(_cpp_execute_include): Don't choose the search chain here.
	Don't call handle_missing_include in the case of an empty
	include chain.
	(_cpp_compare_file_date): Don't choose the search chain here.
	* cpplib.c (do_include_next): Move the in-main-file diagnostic
	here from _cpp_execute_include.  Behave like #include if
	we're in the main file.

From-SVN: r40445