Not compatible with -Zpanic_abort_tests

[alecmocatta]

panic = abort plue -Zpanic_abort_tests results in a forked process per test. At least on macOS, dtrace is not following forks in the executed binary, so it doesn't see the tests actually being run.

cc rust-lang/rust#67650

RUSTFLAGS='-Cpanic=abort -Zpanic_abort_tests' cargo flamegraph --root --test sync

cargo flamegraph --root --test sync

[djc]

I'm not sure if there's something we could do about this within reasonable complexity -- or at least, I probably don't have time/motivation to address this use case, though would be happy to look at a PR if you want to submit one.