Auto merge of #26106 - qrasmont:fix-26088-bhm-opt-in-multiproc, r=gterzian
Auto merge of #26106 - qrasmont:fix-26088-bhm-opt-in-multiproc, r=gterzian

Check the BHM option before starting it in multi-process mode.

In multi-process mode, if the BHM option is set start with one otherwise don't.

I didn't add a test for this. However if I should I'd be happy to be pointed to where similar tests are done (meaning tests of options yielding the expected state) because I didn't find my way in all those tests.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #26088

- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they are minor enough to not require one.

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