Fix segfault with -O2 -fnon-call-exceptions -ftracer

The GIMPLE SSA store merging pass blows up when it is rewriting the
stores because it didn't realize that they don't belong to the same
EH region.  Fixed by refusing to merge them.

	PR tree-optimization/94717
	* gimple-ssa-store-merging.c (try_coalesce_bswap): Return false if
	one of the stores doesn't have the same landing pad number as the
	first.
	(coalesce_immediate_stores): Do not try to coalesce the store using
	bswap if it doesn't have the same landing pad number as the first.