tree-ssa-dse: Fix up go.test/test/fixedbugs/issue16095.go miscompilation [PR100382]

tree-ssa-dse: Fix up go.test/test/fixedbugs/issue16095.go miscompilation [PR100382]

The new DCE code inside of tree DSE removes in -fnon-call-exceptions
go code a load from NULL pointer the testcase relies on throwing an
exception and so the test hangs.

The following patch just repeats a check that e.g. tree-ssa-dce.c
uses to prevent this.

2021-05-03  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/100382
	* tree-ssa-dse.c: Include tree-eh.h.
	(dse_dom_walker::before_dom_children): Don't remove stmts if
	stmt_unremovable_because_of_non_call_eh_p is true.