MATCH: [PR111432] Simplify `a & (x | CST)` to a when we know that (a & ~CST) == 0

MATCH: [PR111432] Simplify `a & (x | CST)` to a when we know that (a & ~CST) == 0

This adds the simplification `a & (x | CST)` to a when we know that
`(a & ~CST) == 0`. In a similar fashion as `a & CST` is handle.

I looked into handling `a | (x & CST)` but that I don't see any decent
simplifications happening.

OK? Bootstrapped and tested on x86_linux-gnu with no regressions.

	PR tree-optimization/111432

gcc/ChangeLog:

	* match.pd (`a & (x | CST)`): New pattern.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/bitops-7.c: New test.