The code here was materializing the value in this case, but then re-loading it, which is unnecessary
since call emission will materialize the value to match the callee's calling convention already.
It does look like a copy into formal evaluation scope is necessary to get the correct lifetimes
in some circumstances. The move-only checker doesn't like any additional copies at all because
it thinks they're consumes, so only borrow in the case where the value is move-only.
