[SCEV] `MatchBinaryOp()`: try to recognize `or` as `add`-in-disguise (w/ no common bits set)

LLVM *loves* to convert `add` of operands with no common bits
into an `or`. But SCEV really doesn't deal with `or` that well,
so try extra hard to recognize this `or` as an `add`.

I believe, previously this wasn't being done because of the recursive
of this, but now that the `createSCEV()` is not recursive,
this should be fine. Unless this is *too* costly compile-time wise...

https://alive2.llvm.org/ce/z/EfapCo