inconsistent exit code on ICE

[matthiaskrgr]

Most of the time, rustc seems to exit with 101, but there are a couple of cases where rust rustc exits with 134

#130015 for example shows exit code 101
but #130104 shows exit code 134

this makes it harder for automated tooling to handle ICEs

[asquared31415]

the exit code 134 error panicked when trying to print the query stack, and then aborted, rather than just exiting due to the ICE panic.