re PR target/89188 (ICE in pre_and_rev_post_order_compute, at cfganal.c:1055)

re PR target/89188 (ICE in pre_and_rev_post_order_compute, at cfganal.c:1055)

	PR target/89188
	* dce.c (delete_unmarked_insns): Don't remove no-op moves if they
	can throw, non-call exceptions are enabled and we can't delete
	dead exceptions or alter cfg.  Set must_clean if
	delete_insn_and_edges returns true, don't set it blindly for calls.
	Assert that delete_unreachable_blocks is called only if can_alter_cfg.

	* g++.dg/opt/pr89188.C: New test.

From-SVN: r268544