bpo-41100: use system libffi for Mac OS 10.15 and up by lawrence-danna-apple · Pull Request #21239 · python/cpython
The vendored libffi sources do not support arm64 Mac OS. Recent versions of mac OS include libffi, including Mac OS 11 on arm64.
This updates setup.py to default to the system libffi on Mac OS 10.15 and forward. It also updates
detect_ctypes to prefer finding libffi in the Xcode SDK, rather than /usr/include
Also, when the Mac OS libffi is used, it removes malloc_closure.c from the sourcs for _ctypes.
libffi already comes with ffi_closure_alloc, and it is not compatible with the one in
malloc_closure.c