Improve contains_p and intersect with bitmasks.

Improve contains_p and intersect with bitmasks.

Improve the way contains_p (wide_int) and intersect behave wioth
singletons and bitmasks.  Also fix a buglet in bitmask_intersect when the
result is a singleton which is not in the current range.

	PR tree-optimization/119039
	gcc/
	* value-range.cc (irange::contains_p): Call wide_int version of
	contains_p for singleton ranges.
	(irange::intersect): If either range is a singleton, use
	contains_p.

	gcc/testsuite/
	* gcc.dg/pr119039-2.c: New.