re PR bootstrap/43858 (Bootstrap failure for powerpc-apple-darwin9: cannot compute suffix of object files)

	From Dominique d'Humieres <dominiq@lps.ens.fr>
	PR bootstrap/43858
	* ifcvt.c (dead_or_predicable): Use df_simulate_find_defs to compute
	test_set.

From-SVN: r158898