Add an option not to fail on version mismatch

[trailofbits]

Add an option not to fail on version mismatch

[woodruffw]

Sorry, but I don't think we want support for this: CPython's maintainers can always retroactively specify an ABI member for older CPython versions, but it would be unsound in the general case for us to assume that stable ABI members were stable from their introduction version, rather than their stabilization version.

If the wheel are correctly tested, it will never be a source of bugs and allows a broader range of python versions to be supported with a single wheel.

These things are difficult to correctly test, because they can involve undefined behavior: an ABI member might be "unchanged" before stabilization, but prior versions might not be const-correct or might have different parameter behavior, for example. The program as compiled might behave as expected, but that would be purely incidental and subject to changes to the compiler.

Out of curiosity: are you aware of people intentionally setting their ABI3 version lower than is correct, based on the assumption that the function's presence + similar parameters imply that it hasn't changed? I don't think that's a use case that I want to encourage 🙂