tree-optimization/127390 - vectorization of _BitInt comparisons

We fail to reject vectorizing of comparisons of non-mode precision
integer types.  Those need to be dealt with via bitfield lowering
in ifcvt or pattern recognition.

	PR tree-optimization/127390
	* tree-vect-stmts.cc (vectorizable_comparison_1): Reject
	bit-precision integer comparisons.

	* gcc.dg/vect/vect-pr127390.c: New testcase.