* cppexp.c (parse_defined): Mark macro used.
	* cpphash.h (struct cpp_macro): New member "used".
	(_cpp_mark_macro_used, _cpp_warn_if_unused_macro): New.
	(struct cpp_reader): New member.
	* cppinit.c (cpp_finish_options): Set first_unused_line.
	(cpp_finish): Warn of unused macros if requested.
	(OPT_TABLE): New switches.
	(cpp_handle_option): Handle them.
	* cpplib.c (do_undef): Warn if macro unused.
	(do_ifdef, do_ifndef): Mark macro used.
	* cpplib.h (struct cpp_options): New member.
	* cppmacro.c (_cpp_warn_if_unused_macro): New.
	(enter_macro_context): Mark macro used.
	(_cpp_create_definition): Mark macro unused; warn if unused
	when redefined.
	* cpptrad.c (scan_out_logcial_line, push_replacement_text):
	Mark macros used.
	* doc/cppopts.texi: Update.
testsuite:
	* gcc.dg/cpp/trad/Wunused.c, gcc.dg/cpp/trad/Wunused.h,
	gcc.dg/cpp/Wunused.c, gcc.dg/cpp/Wunused.h: New tests.

From-SVN: r55692