Fix PR 110666: `(a != 2) == a` produces wrong code

Fix PR 110666: `(a != 2) == a` produces wrong code

I had messed up the case where the outer operator is `==`.
The check for the resulting should have been `==` and not `!=`.
This patch fixes that and adds a full runtime testcase now for
all cases to make sure it works.

OK? Bootstrapped and tested on x86-64-linux-gnu with no regressions.

gcc/ChangeLog:

	PR tree-optimization/110666
	* match.pd (A NEEQ (A NEEQ CST)): Fix Outer EQ case.

gcc/testsuite/ChangeLog:

	PR tree-optimization/110666
	* gcc.c-torture/execute/pr110666-1.c: New test.