[18.x] Add ROOT patches

[chrisburr]

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/13052121337. Examine the logs at this URL for more detail.}

[h-vetinari]

I haven't reviewed the patches, but the rest looks fine (assuming CI passes).

PS. Since this is purely additive configuration, a build number bump wouldn't have been necessary, but whatever. :)

[h-vetinari]

I was following this patch along - it's finally been merged (llvm/llvm-project@20e9049) for llvm 20. :)

[chrisburr]

Thanks for taking a look! Looks like this is working locally for me now with ROOT so I'll merge it when the CI finishes.

PS. Since this is purely additive configuration, a build number bump wouldn't have been necessary, but whatever. :)

I'm so used to ROOT lagging behind LLVM that the build hashes change for unrelated reasons by the time ROOT gets to a given version 😆 It's nice that that is no longer the case.

[h-vetinari]

I'm so used to ROOT lagging behind LLVM that the build hashes change for unrelated reasons by the time ROOT gets to a given version 😆 It's nice that that is no longer the case.

It's good practice for sure, and it can still happen that hashes changes tec.. But root is definitely closing the gap, and we had just rebuilt the 18.x branch: #336 (also llvm 18 is still our default compiler stack; might be a first that root catches up to that 🥳)