options: Adjust cl_optimization_compare to avoid checking ICE [PR115913]

At the end of a sequence like:
 #pragma GCC push_options
 ...
 #pragma GCC pop_options

the handler for pop_options calls cl_optimization_compare() (as generated by
optc-save-gen.awk) to make sure that all global state has been restored to
the value it had prior to the push_options call. The verification is
performed for almost all entries in the global_options struct. This leads to
unexpected checking asserts, as discussed in the PR, in case the state of
warnings-related options has been intentionally modified in between
push_options and pop_options via a call to #pragma GCC diagnostic. Address
that by skipping the verification for CL_WARNING-flagged options.

gcc/ChangeLog:

	PR middle-end/115913
	* optc-save-gen.awk (cl_optimization_compare): Skip options with
	CL_WARNING flag.

gcc/testsuite/ChangeLog:

	PR middle-end/115913
	* c-c++-common/cpp/pr115913.c: New test.