[20.x] Add patches for ROOT 6.38.00

[vepadulano]

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For recipe/meta.yaml:

• ℹ️ The recipe is not parsable by parser conda-souschef (grayskull). This parser is not currently used by conda-forge, but may be in the future. We are collecting information to see which recipes are compatible with grayskull.
• ℹ️ The recipe is not parsable by parser conda-recipe-manager. The recipe can only be automatically migrated to the new v1 format if it is parseable by conda-recipe-manager.

_{This message was generated by GitHub Actions workflow run https://github.com/conda-forge/conda-forge-webservices/actions/runs/19757094887. Examine the logs at this URL for more detail.}

[h-vetinari]

This LGTM.

It bears repeating though that clang 20 has a bunch of ABI breaks (especially in C++ containers), and we've tried avoid using this at scale, c.f. conda-forge/conda-forge-pinning-feedstock#7839

In other words, it's possible you'll get issues when you combine llvm-20-based root with packages built by llvm 19 or 21 (which fixed the ABI break)

[vepadulano]

@h-vetinari thank you for your comment, if we'll see some issues at least we know where to start looking from. Meanwhile, I removed the leftover comment from conda_build_config.yaml

[h-vetinari]

I added this file on the main branch in 7613f51, so we don't have to check this in anew every time root adds support for a version

[vepadulano]

Thank you so much!