This commit fixes Building wheel for cffi (setup.py) ... error:
c/_cffi_backend.c:15:10: fatal error: ffi.h: No such file or directory
some python packages do not offer precompiled binary packages for aarch64 on PyPI.
only happens on non-amd64 arches, so add [!amd64].
Signed-off-by: JiangYu <lnsyyj@hotmail.com>