Fix PR 108582: ICE due to PHI-OPT removing a still in use ssa_name.

Fix PR 108582: ICE due to PHI-OPT removing a still in use ssa_name.

This patch adds a check in match_simplify_replacement to make sure the middlebb
does not have any phi-nodes as we don't currently move those.
This was just a thinko from before.

Ok? Bootstrapped and tested on x86_64-linux-gnu with no regressions?

	PR tree-optimization/108582

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (match_simplify_replacement): Add check
	for middlebb to have no phi nodes.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr108582-1.c: New test.