We were hitting a translation error for imul in another application - this test
case is a reduced example demonstrating the problem.
The root cause was that there were a few missing cases for the new signed
immediate values from flexdis; this caused a fallthrough that mis-identified
signed immediates as non-immediates, triggering an error.
Previously, we asked macaw to discover three functions in the tail-call
test. One of those only ever appeared as a tail call from another
function; currently macaw isn't smart enough to discover that as its own
function (and that's probably okay for now).
