[InstCombine] Fold signbit test of a pow2 or zero

(X & X) <  0 --> X == MinSignedC
(X & X) > -1 --> X != MinSignedC

Alive2: https://alive2.llvm.org/ce/z/_J5q3S
Closes: https://github.com/llvm/llvm-project/issues/60957



Signed-off-by: Jun Zhang <jun@junz.org>

Differential Revision: https://reviews.llvm.org/D144777