Don't warn about missing noreturn for main

[Richard Henderson]

> 	* cp/decl.c (cp_missing_noreturn_ok_p): New.
> 	(init_decl_processing): Set lang_missing_noreturn_ok_p.
> 	* 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.
> 	* gcc.dg/noreturn-3.c: New test.
> 	* gcc.dg/noreturn-4.c: New test.

Ok.


r~