match: Add `cmp - 1` simplification to `-icmp` [PR110949]

match: Add `cmp - 1` simplification to `-icmp` [PR110949]

I have seen this a few places though the testcase from PR 95906
is an obvious place where this shows up for sure.
This convert `cmp - 1` into `-icmp` as that form is more useful
in many cases.

Changes since v1:
* v2: Add check for outer type's precision being greater than 1.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/110949
	PR tree-optimization/95906

gcc/ChangeLog:

	* match.pd (cmp - 1): New pattern.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/cmp-2.c: New test.
	* gcc.dg/tree-ssa/max-bitcmp-1.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>