gh-125498: Update JIT builds to use LLVM 19 and use preserve_none

[savannahostrowski]

• Issue: Replace ghccc with preserve_none in JIT builds #125498
• Issue: Update JIT compilation to use LLVM 19 #123714

[savannahostrowski]

So it looks like the Python version installed with brew is failing transitively...doing a bit of spelunking here.

[savannahostrowski]

Okay, after a bit of digging here, my cursory diagnosis around the failing x86 macOS runs is essentially this (and I am by no means a Homebrew or Ruby expert):
- The default Python version of Homebrew was recently updated to 3.13 (see Homebrew/homebrew-core#182840). As part of this PR, the formula for Python 3.13 seem to vastly differ from 3.12...and 3.12 was also updated.
It seems like Homebrew is no longer handling overwriting files in the way it once did. More specifically, the combo of the setup-python step and then brew installing Python (via LLVM) is not cooperating. I did some testing here, and it looks like this issue only happens with 3.12 onward (preliminary run of https://github.com/savannahostrowski/test_repo_python_install/actions/runs/11453722971 but waiting on the fail-fast: false run for the full output).

Update as of 10/22:
I got a reply from a Homebrew maintainer: Homebrew/homebrew-core#195288. It looks like this is a known GHA issue that has existed since at least May and started popping up recently as a result of some updates that GitHub made to runner images. The workaround is to remove the symlink to the pre-installed Python so that Homebrew Python is used instead. They may also start investigating overwriting the symlinks when in GHA context on their end because this seems to be a prevalent issue.

[brandtbucher]

Looks good, just a few opportunities to tidy things up:

[savannahostrowski]

Oooo, thanks for the review @brandtbucher. Great catches for cleaning things up a bit. Much simpler.

[brandtbucher]

Awesome! @mdboom, I'm landing this, so we should probably also update the benchmark runners that need it. Let me know if you want help.

[mdboom]

Awesome! @mdboom, I'm landing this, so we should probably also update the benchmark runners that need it. Let me know if you want help.

Yep -- I'll do that now.