Add unchecked_shl/shr check for intrinsics to fix miri's test suit
r? @RalfJung
cc @oli-obk
#53697 broke miri's test suite as described in [this comment](https://github.com/rust-lang/rust/pull/53697#issuecomment-419034668). This PR adds test for the `unchecked_shr/shl` for the intrinsics.