Deal with prior EH/abormal cleanup when fixing up noreturn calls

When a dead EH or abnormal edge makes a call queued for noreturn fixup
unreachable, just skip processing it.

	PR tree-optimization/121870
	* tree-ssa-propagate.cc
	(substitute_and_fold_engine::substitute_and_fold): Skip
	removed stmts from noreturn fixup.

	* g++.dg/torture/pr121870.C: New testcase.

(cherry picked from commit 5c4f1313e753aeb6920a48c62c7c99ad36e1adae)
2 files changed