PR c/10604

	* c-common.c (warn_sign_compare): Initialize to -1.
	* c-opts.c (c_common_init_options): Don't set warn_sign_compare here.
	(c_common_decode_option <OPT_Wall>): Set warn_sign_compare
	for C++ only.
	(c_common_post_options): Set warn_sign_compare from extra_warnings
	if it's still -1 at this point.

	* toplev.c (maybe_warn_unused_parameter): New static variable.
	(set_Wextra): New static function.
	(W_options): Remove "extra".
	(decode_W_option): Call set_Wextra.
	(independent_decode_option): Likewise.
	(set_Wunused): Cooperate with set_Wextra in setting
	warn_unused_parameter.
	(rest_of_compilation): No need to check extra_warnings as
	well as warn_uninitialized.

	* c-typeck.c (build_binary_op, build_conditional_expr):
	No need to check extra_warnings as well as warn_sign_compare.
	(internal_build_compound_expr): No need to check extra_warnings
	as well as warn_unused_value.
	* function.c (expand_function_end): No need to check extra_warnings
	as well as warn_unused_parameter.
	* stmt.c (expand_expr_stmt_value): No need to check extra_warnings
	as well as warn_unused_value.
	* cp/typeck.c (build_x_compound_expr): No need to check
	extra_warnings as well as warn_unused_value.

	* doc/invoke.texi: Clarify documentation of -Wsign-compare.
	* gcc.dg/compare7.c, g++.dg/warn/compare1.C: New testcases.

	* Makefile.in: Disable -Werror for gengtype-lex.o.

From-SVN: r66436