These cases were discovered through various attempts to elide more loads
and stores after a branch has already occurred.

Also implement operator!= for Pointer<T>, and remove the redundant
Nucleus:createPtrEQ() which both LLVM and Subzero support through
integer value comparison.

Bug: b/180131694
Change-Id: I27c86b4fcbe6e1740801e40cb6877629f01d6540
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/52929
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>