Allow IPA_CP to handle UNDEFINED as VARYING.

When applying a bitmask to reflect ranges, it is sometimes deferred and
this can result in an UNDEFINED result.  IPA is not expecting this, and
add a check for it, and convert to VARYING if encountered.

	PR tree-optimization/120048
	gcc/
	* ipa-cp.cc (ipcp_store_vr_results): Check for UNDEFINED.

	gcc/testsuite/
	* gcc.dg/pr120048.c: New.