Fix test isolation for stateful configurations in the testsuite

[sklam]

This fixes a SIGILL detected in conda-forge/numba-feedstock#131 by adding needed isolation to test that changes the target machine.

Minimal reproducer is:

python runtests.py numba.tests.test_vectorization.TestVectorization.test_nditer_loop numba.tests.test_withlifting.TestLiftObj.test_case02_mutate_array_ahead_of_ctx

[sklam]

I have confirmed that it passes with conda-forge build-locally.py for a previously failing config.

[stuartarchibald]

@sklam suggest changing the PR title to something like "Fix test isolation for stateful configurations" or something like that?

[stuartarchibald]

Thanks for the patch @sklam. I checked the test suite for uses of override_env_config where an overridden env var is likely to impact machine code generation, it seems like this patch isolates all remaining cases which weren't already covered. As noted OOB there's still a potential issue with the use of the fast flag, but this is better resolved through fixing #7168. There's one minor comment to resolve else looks good. Thanks again!

[stuartarchibald]

Note: l4604 of this file has overrides.append(override_env_config(k, v)) which, by virtue of its use, is also creating skylake ISA specific machine code, however, all the tests in this test class are in subprocesses so it is "safe".

[sklam]

Actually, it needed the run_in_subprocess for all test methods or else it fail: https://dev.azure.com/numba/numba/_build/results?buildId=16609&view=logs&j=7d262216-4420-5164-53df-7079f36c65da&t=9212e158-8292-5264-48bf-03dbdfc6e73f&l=712

[stuartarchibald]

Thanks for the update. This is approved conditional on CI passing once main is stable again.

[stuartarchibald]

Re-approve following merge of main into this branch.