building numpy from source code fails on arm64 because of missing dependency Cython.

ModuleNotFoundError: No module named 'Cython'

Reproducing code example:

python setup.py bdist_wheel

Error message:

Running setup.py bdist_wheel for numpy: started
Running setup.py bdist_wheel for numpy: finished with status 'error'
Complete output from command /usr/bin/python3 -u -c "import setuptools, tokenize;file='/tmp/pip-build-u485u_8l/numpy/setup.py';f=getattr(tokenize, 'open', open)(file);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, file, 'exec'))" bdist_wheel -d /tmp/tmpijsuuig2pip-wheel- --python-tag cp36:
Running from numpy source directory.
Cythonizing sources
Processing numpy/random/_bounded_integers.pxd.in
Processing numpy/random/_philox.pyx
Traceback (most recent call last):
File "/tmp/pip-build-u485u_8l/numpy/tools/cythonize.py", line 61, in process_pyx
from Cython.Compiler.Version import version as cython_version
ModuleNotFoundError: No module named 'Cython'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/tmp/pip-build-u485u_8l/numpy/tools/cythonize.py", line 238, in
main()
File "/tmp/pip-build-u485u_8l/numpy/tools/cythonize.py", line 234, in main
find_process_files(root_dir)