libstdc++: Fix lifetime bugs for non-TLS eh_globals [PR105880]

libstdc++: Fix lifetime bugs for non-TLS eh_globals [PR105880]

This ensures that the single-threaded fallback buffer eh_globals is not
destroyed during program termination, using the same immortalization
technique used for error category objects.

Also ensure that init._M_init can still be read after init has been
destroyed, by making it a static data member.

libstdc++-v3/ChangeLog:

	PR libstdc++/105880
	* libsupc++/eh_globals.cc (eh_globals): Ensure constant init and
	prevent destruction during termination.
	(__eh_globals_init::_M_init): Replace with static member _S_init.
	(__cxxabiv1::__cxa_get_globals_fast): Update.
	(__cxxabiv1::__cxa_get_globals): Likewise.