To dodge the versioned dependency conflict audit, I've added `coind3d`,
`gjs`, `pyside` and `pyside@2` to the allowlist. It's very unlikely that
these formulae use LLVM's Python bindings. LLVM is keg-only, and we
don't modify `PYTHONPATH`, so these formulae shouldn't even be able to
find LLVM's Python bindings.
However, just in case, I've also installed LLVM's Python bindings for
multiple versions of Python3. (This doesn't include LLDB, which has
linkage with the Python framework, which ties it to a specific Python
version.)
While we're here:
- remove duplication from the installed Xcode toolchain
- fix some version references so that they work for HEAD installs too
We clean up the duplication by installing the Xcode toolchain manually.
Closes#87483.