tree-optimization/116057 - wrong code with CCP and vector CTORs

The following fixes an issue with CCPs likely_value when faced with
a vector CTOR containing undef SSA names and constants.  This should
be classified as CONSTANT and not UNDEFINED.

	PR tree-optimization/116057
	* tree-ssa-ccp.cc (likely_value): Also walk CTORs in stmt
	operands to look for constants.

	* gcc.dg/torture/pr116057.c: New testcase.