c-decl.c (c_decode_option): Remove support of -Wmissing-noreturn.

	* c-decl.c (c_decode_option): Remove support of
	-Wmissing-noreturn.

	* toplev.c (documented_lang_options): Remove -Wmissing-noreturn.
	(W_options): Add -Wmissing-noreturn here.

	* flow.c: Define lang_missing_noreturn_ok_p.
	(check_function_return_warnings): Use it.

	* c-common.h: Declare lang_missing_noreturn_ok_p.

	* c-lang.c (c_missing_noreturn_ok_p): New function.
	(lang_init): Set lang_missing_noreturn_ok_p.

	* invoke.texi (Warning Options): Document this.

From-SVN: r38612