vect/ifcvt: Add vec_cond fallback and check for vector versioning.

vect/ifcvt: Add vec_cond fallback and check for vector versioning.

This restricts tree-ifcvt to only create COND_OPs when we versioned the
loop for vectorization.  Apart from that it re-creates a VEC_COND_EXPR
in vect_expand_fold_left if we emitted a COND_OP.

gcc/ChangeLog:

	PR tree-optimization/112361
	PR target/112359
	PR middle-end/112406

	* tree-if-conv.cc (convert_scalar_cond_reduction): Remember if
	loop was versioned and only then create COND_OPs.
	(predicate_scalar_phi): Do not create COND_OP when not
	vectorizing.
	* tree-vect-loop.cc (vect_expand_fold_left): Re-create
	VEC_COND_EXPR.
	(vectorize_fold_left_reduction): Pass mask to
	vect_expand_fold_left.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr112359.c: New test.