Improve multiplication by powers of 2 in range-ops.

Improve multiplication by powers of 2 in range-ops.

For unsigned numbers, multiplication by X, where X is a power of 2 is
[0,0][X,+INF].

This patch causes a regression to g++.dg/pr71488.C where
-Wstringop-overflow gets the same IL as before, but better ranges
cause it to issue a bogus warning.  I will create a PR with some
notes.

No discernible changes in performance.

Tested on x86-64 Linux.

	PR tree-optimization/55157

gcc/ChangeLog:

	* range-op.cc (operator_mult::wi_fold): Optimize multiplications
	by powers of 2.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr55157.c: New test.