Add a directive to control the expected exit code for compilation #356
Description
Currently, the expected exit-status for compilation seems to be hard-coded. The exist status for running the program can be controlled via @run:100, but in Miri we don't run the program (not in the way ui test thinks, anyway), so this does not help us there.
Or maybe the better fix is to make it so that in the Miri test suite, ui_test skips the "compile" part and considers invoking Miri to be the actual "run" step?