[PR31531] MATCH: Improve ~a < ~b and ~a < CST, allow a nop cast inbetween ~ and a/b

[PR31531] MATCH: Improve ~a < ~b and ~a < CST, allow a nop cast inbetween ~ and a/b

Currently we able to simplify `~a CMP ~b` to `b CMP a` but we should allow a nop
conversion in between the `~` and the `a` which can show up. A similarly thing should
be done for `~a CMP CST`.

I had originally submitted the `~a CMP CST` case as
https://gcc.gnu.org/pipermail/gcc-patches/2021-November/585088.html;
I noticed we should do the same thing for the `~a CMP ~b` case and combined
it with that one here.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

	PR tree-optimization/31531

gcc/ChangeLog:

	* match.pd (~X op ~Y): Allow for an optional nop convert.
	(~X op C): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr31531-1.c: New test.
	* gcc.dg/tree-ssa/pr31531-2.c: New test.