cppopts.texi (-dU): Document.

gcc:
	* doc/cppopts.texi (-dU): Document.
	* c-common.h (flag_dump_macros): Update comment.
	* c-opts.c (handle_OPT_d): Handle -dU.
	* c-ppoutput.c (macro_queue, define_queue, undef_queue,
	dump_queued_macros, cb_used_define, cb_used_undef): New.
	(init_pp_output): Handle -dU.
	(cb_line_change): Call dump_queued_macros.
	* toplev.c (decode_d_option): Accept -dU as preprocessor option.

gcc/testsuite:
	* gcc.dg/cpp/cmdlne-dU-1.c, gcc.dg/cpp/cmdlne-dU-2.c,
	gcc.dg/cpp/cmdlne-dU-3.c, gcc.dg/cpp/cmdlne-dU-4.c,
	gcc.dg/cpp/cmdlne-dU-5.c, gcc.dg/cpp/cmdlne-dU-6.c,
	gcc.dg/cpp/cmdlne-dU-7.c, gcc.dg/cpp/cmdlne-dU-8.c,
	gcc.dg/cpp/cmdlne-dU-9.c, gcc.dg/cpp/cmdlne-dU-10.c,
	gcc.dg/cpp/cmdlne-dU-11.c, gcc.dg/cpp/cmdlne-dU-12.c,
	gcc.dg/cpp/cmdlne-dU-13.c, gcc.dg/cpp/cmdlne-dU-14.c,
	gcc.dg/cpp/cmdlne-dU-15.c, gcc.dg/cpp/cmdlne-dU-16.c,
	gcc.dg/cpp/cmdlne-dU-17.c, gcc.dg/cpp/cmdlne-dU-18.c,
	gcc.dg/cpp/cmdlne-dU-19.c, gcc.dg/cpp/cmdlne-dU-20.c,
	gcc.dg/cpp/cmdlne-dU-21.c, gcc.dg/cpp/cmdlne-dU-22.c: New tests.

libcpp:
	* include/cpplib.h (struct cpp_callbacks): Add used_define,
	used_undef and before_define.
	(NODE_USED): Define.
	* directives.c (do_define, do_undef, undefine_macros, do_ifdef,
	do_ifndef, cpp_pop_definition): Handle new flag and use new
	callbacks.
	* expr.c (parse_defined): Handle new flag and use new callbacks.
	* macro.c (enter_macro_context, _cpp_free_definition): Handle new
	flag and use new callbacks.

From-SVN: r133847