language/python: avoid modifying all Python symlinks

[cho-m]

Homebrew Python will always have a realpath in HOMEBREW_CELLAR. Instead, check if the symlink target points to HOMEBREW_CELLAR.

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

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Main goals is to retain valid symlinks like python3 -> #{Formula["[email protected]"].opt_bin}/python3 otherwise the existing logic rewrites to Framework path on macOS which will always differ from Linux.

Still some other differences that need to be fixed up to improve all bottle chance, e.g.

• lib64 symlink on Linux
• Realpath executable saved in pyvenv.cfg

[MikeMcQuaid]

Good catch, thanks again @cho-m!