tree-optimization/67196 - normalize use predicates earlier

The following makes sure to have use predicates simplified and
normalized before doing uninit_analysis::overlap because that
otherwise cannot pick up all flag setting cases.  This fixes
half of the issue in PR67196 and conveniently resolves the
XFAIL in gcc.dg/uninit-pred-7_a.c.

	PR tree-optimization/67196
	* gimple-predicate-analysis.cc (uninit_analysis::is_use_guarded):
	Simplify and normalize use prediates before first use.

	* gcc.dg/uninit-pred-7_a.c: Un-XFAIL.