Lots of python packages seem to ship their source distributions with
generated code. In recent cython versions there is a way to force a
regeneration of these files and using it sounds generally sounds like a
good thing.
If it turns out, that this causes problems on individual packages,
setting `dontForceRegenCython` will prevent the regeneration.
Added in 3.0.0a11 and backported to 2.9.34, so both cython versions we
ship right now support this flag.
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