Inline unsupported_range constructor.

An unsupported_range temporary is instantiated in every Value_Range
for completeness sake and should be mostly a NOP.  However, it's
showing up in the callgrind stats, because it's not inline.  This
fixes the oversight.

	PR tree-optimization/106514

gcc/ChangeLog:

	* value-range.cc (unsupported_range::unsupported_range): Move...
	* value-range.h (unsupported_range::unsupported_range): ...here.
	(unsupported_range::set_undefined): New.