Linker on macOS prints excessive warnings in CI

[straight-shoota]

The linker on macOS prints such as warning for every individual object file:

ld: warning: object file (I-O-5858B-yteF-ormat5858B-igE-ndian.o0.o) was built for newer macOS version (14.0) than being linked (11.0)

Example CI run: https://github.com/crystal-lang/crystal/actions/runs/11521615235/job/32075666471?pr=15127

The log is spammed with about ~87k of these warnings, which is just excessive. It's basically unusable through the GitHub web UI. You can still download the entire job log as a text file.

Anyway, we should not get that many warnings.
Ideally, we need to fix this. Or at least silence the warnings.

I'm not familiar with macOS build system, so I'm not sure what this warning even means or what we're suppose to do.

This has previously been mentioned in #14835

[beta-ziliani]

This is likely an instance of #13846, although I thought it was fixed with #14466

[straight-shoota]

We might want to try using a new version of LLVM (#14651).

[straight-shoota]

Updating to LLVM 18.1 does not make the warnings go away. Was worth a try 🤷

[will]

For what it's worth, I'm getting this locally again with 1.14 on an arm mac on macos 15.1