tree-optimization/101868 - avoid PRE of trapping mems across calls

tree-optimization/101868 - avoid PRE of trapping mems across calls

This backports a fix for the omission of a check of trapping mems
when hoisting them across calls that might not return.  This was
originally done as part of a fix to handle const functions that throw
properly.

2021-08-17  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101373
	PR tree-optimization/101868
	* tree-ssa-pre.c (prune_clobbered_mems): Also prune trapping
	references when the BB may not return.

	* gcc.dg/lto/pr101868_0.c: New testcase.
	* gcc.dg/lto/pr101868_1.c: Likewise.
	* gcc.dg/lto/pr101868_2.c: Likewise.
	* gcc.dg/lto/pr101868_3.c: Likewise.

(cherry picked from commit ee875b63b22e30a0dcb4b05f7532c2c416ba6cd0)