libcython: use Python's libexec/"bin" directory

[carlocab]

Needed for #107517.

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[cho-m]

Not sure why error is happening on Python 3.9. I think it is related to updating setuptools resource (which may have modified bundled distutils), but it is using same version as Python 3.10.

/opt/homebrew/lib/python3.9/site-packages/setuptools/command/install.py:34: SetuptoolsDeprecationWarning: setup.py install is deprecated. Use build and pip and other standards-based tools.
    warnings.warn(
  error: [Errno 2] No such file or directory: 'brew'

It could be trying to run a brew command but not finding command on PATH.

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Also hit this on #107066 but I thought it was isolated to that PR so I just switched to stdlib distutils. Looks like there may be something else going wrong.

[cho-m]

Maybe https://github.com/pypa/setuptools/blob/main/setuptools/_distutils/command/_framework_compat.py#L45 ?

    homebrew_prefix = subprocess.check_output(['brew', '--prefix'], text=True).strip()

[carlocab]

Same conclusion at #107662.

[carlocab]

Testing an inreplace workaround.