PHIOPT: Ignore predicates for match-and-simplify phi-opt

PHIOPT: Ignore predicates for match-and-simplify phi-opt

This fixes a missed optimization where early phi-opt would
not work when there was predicates. The easiest fix is
to change empty_bb_or_one_feeding_into_p to ignore those
statements while checking for only feeding statement.

Note phi-opt-23.c and phi-opt-24.c still fail as we don't handle
diamond form in match_and_simplify phiopt yet.

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

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (empty_bb_or_one_feeding_into_p):
	Instead of calling last_and_only_stmt, look for the last statement
	manually.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/ssa-ifcombine-13.c: Add -fno-ssa-phiopt.