tree-optimization/112344 - wrong final value replacement

tree-optimization/112344 - wrong final value replacement

When performing final value replacement chrec_apply that's used to
compute the overall effect of niters to a CHREC doesn't consider that
the overall increment of { -2147483648, +, 2 } doesn't fit in
a signed integer when the loop iterates until the value of the IV
of 20.  The following fixes this mistake, carrying out the multiply
and add in an unsigned type instead, avoiding undefined overflow
and thus later miscompilation by path range analysis.

	PR tree-optimization/112344
	* tree-chrec.cc (chrec_apply): Perform the overall increment
	calculation and increment in an unsigned type.

	* gcc.dg/torture/pr112344.c: New testcase.