MATCH: [PR109959] `(uns <= 1) & uns` could be optimized to `uns == 1`

I noticed while looking into some code generation of bitmap_single_bit_set_p,
that sometimes:
```
  if (uns > 1)
    return 0;
  return uns == 1;
```
Would not optimize down to just:
```
return uns == 1;
```

In this case, VRP likes to change `a == 1` into `(bool)a` if
a has a range of [0,1] due to `a <= 1` side of the branch.
We might end up with this similar code even without VRP,
in the case of builtin-sprintf-warn-23.c (and Wrestrict.c), we had:
```
if (s < 0 || 1 < s)
  s = 0;
```
Which is the same as `s = ((unsigned)s) <= 1 ? s : 0`;
So we should be able to catch that also.

This adds 2 patterns to catch `(uns <= 1) & uns` and
`(uns > 1) ? 0 : uns` and convert those into:
`(convert) uns == 1`.

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

	PR tree-optimization/109959

gcc/ChangeLog:

	* match.pd (`(a > 1) ? 0 : (cast)a`, `(a <= 1) & (cast)a`):
	New patterns.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/builtin-sprintf-warn-23.c: Remove xfail.
	* c-c++-common/Wrestrict.c: Update test and remove some xfail.
	* gcc.dg/tree-ssa/cmpeq-1.c: New test.
	* gcc.dg/tree-ssa/cmpeq-2.c: New test.
	* gcc.dg/tree-ssa/cmpeq-3.c: New test.