Combine new calculated ranges with existing range.

When a range is recalculated, retain what was previously known as IL changes
can produce different results from un-executed code.   This also paves
the way for external injection of ranges.

	gcc/
	PR tree-optimization/97737
	PR tree-optimization/97741
	* gimple-range.cc: (gimple_ranger::range_of_stmt): Intersect newly
	calculated ranges with the existing known global range.
	gcc/testsuite/
	* gcc.dg/pr97737.c: New.
	* gcc.dg/pr97741.c: New.