[patch] New flag -Wsystem-headers

[Benjamin Kosnik]

This patch is now in.

Hopefully, this will make the shadow header work for libstdc++-v3 easier.

bootstrapped on x86/linux

Thanks Branko!

-benjamin


2000-09-25 Branko Cibej <branko.cibej@hermes.si>

        * flags.h:  Declare warning flag warn_system_headers.
        * toplev.c:  Define it.
        (W_options): Add option -Wsystem-headers.
        * diagnostic.c (count_error): Test warn_system_headers.
        * invoke.texi:  Add description for -Wsystem-headers.
	* cpplib.h (cpp_options): New member warn_system_headers.
	* cpphash.h (CPP_PEDANTIC, CPP_WTRADITIONAL): Don't test
	CPP_IN_SYSTEM_HEADER.
	* cpplib.c (do_import, do_pragma_once): Likewise.
	* cpperror.c (_cpp_begin_message): Test warn_system_headers
	and CPP_IN_SYSTEM_HEADER.
	* cppinit.c (handle_option): Recognize -Wsystem_headers.
	(print_help): Describe -Wsystem_headers.
	* cpplex.c (lex_line): Reorganize condition so that warnings
	about C++ comments in system headers can be enabled. Remove
	label do_line_comment.