Remove OMP_NUM_THREADS if set to empty

[mrocklin]

Generally though, sometimes our use of OMP_NUM_THREADS makes other systems sad. It's unfortunately somewhat difficult to turn off. A common approach is that people set OMP_NUM_THREADS="" but this doesn't properly unset things.

I'm curious if an approach like this would be helpful.

There might be a cleaner way to do this, and this might be a bad idea. Please feel free to reject. It was just easy to put this up as a PR.

@ntabris would something like this make your life easier? @fjetter is this not dumb?

[ntabris]

would something like this make your life easier?

Not anytime soon but seems like a positive change to me.

[github-actions[bot]]

Unit Test Results

_See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests._

    25 files  ± 0      25 suites  ±0   10h 21m 20s ⏱️ + 7m 36s  4 129 tests + 1   4 015 ✅ +1    110 💤 ±0   4 ❌ ± 0  47 680 runs  +12  45 574 ✅ +1  2 088 💤 ±0  18 ❌ +11 

For more details on these failures, see this check.

Results for commit e8d9b815. ± Comparison against base commit 29530909.

[fjetter]

No objections. It appears to not be working, though. The test is failing (linter is also off)