Finish cleanup/removing -Wstrict-overflow= support [PR125558]

This finishes removing the support for -Wstrict-overflow that seemly was
missed before. It also marks the option as being ignored and fixes
the -Wstrict-overflow= case where it was rejecting -Wstrict-overflow=1 now.

Pushed as obvious after bootstrap/test on x86_64-linux-gnu.

	PR middle-end/125558

gcc/ChangeLog:

	* common.opt (Wstrict-overflow): Mark as Ignore.
	(Wstrict-overflow=): Fix up and mark as igore.
	* gcc-diagnostic-spec.cc (nowarn_spec_t::nowarn_spec_t):
	Remove OPT_Wstrict_overflow.
	* opts.cc (common_handle_option): Likewise.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>