re PR libgcc/71744 (Concurrently throwing exceptions is not scalable)

re PR libgcc/71744 (Concurrently throwing exceptions is not scalable)

	PR libgcc/71744
	* unwind-dw2-fde.c (ATOMIC_FDE_FAST_PATH): Define if __register_frame*
	is not the primary registry and atomics are available.
	(any_objects_registered): New variable.
	(__register_frame_info_bases, __register_frame_info_table_bases):
	Atomically store 1 to any_objects_registered after registering first
	unwind info.
	(_Unwind_Find_FDE): Return early if any_objects_registered is 0.

From-SVN: r240193