sandbox: fix DeathMessage tests in official builds
sandbox: fix DeathMessage tests in official builds

It seems that official builds now use the "ud2" instruction to handle
CHECK failures, which causes the process to exit due to SIGILL instead
of SIGABRT. Unclear at the moment exactly why (maybe a toolchain
change?), but easy to workaround for now.

TBR=jln@chromium.org
BUG=612507

Review-Url: https://codereview.chromium.org/1994303002
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#394867}

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