Fix factor_out_conditional_operation heuristics for constants

Fix factor_out_conditional_operation heuristics for constants

While working on a different patch, I noticed the heuristics were not
doing the right thing if there was statements before the NOP/PREDICTs.
(LABELS don't have other statements before them).

This fixes that oversight which was added in r15-3334-gceda727dafba6e.

Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (factor_out_conditional_operation): Instead
	of just ignorning a NOP/PREDICT, skip over them before checking
	the heuristics.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>