fix macos 15.4.1 build

[greatgitsby]

resolves: https://github.com/commaai/openpilot/pull/35104

pending: https://github.com/commaai/opendbc/pull/2180 https://github.com/commaai/panda/pull/2196

macos-latest isn't on 15+ yet. adding macos-15 to CI to enforce build success

[adeebshihadeh]

@sshane you remember why we didn't want to use clang for macOS?

[sshane]

I don't think I was involved in that decision at all, no clue

[adeebshihadeh]

Can you evaluate and merge if it makes sense?

[greatgitsby]

old ref, maybe an unsupported compiler flag: https://github.com/commaai/panda/pull/1241

newer ref from @fredyshox: https://github.com/commaai/panda/pull/1409

EDIT: the original reason was build failure. there are no build failures with normal gcc/clang now because all the compiler flags are supported. this change is fine.

[greatgitsby]

clang17 supports -std=gnu11 which was the original complaint.

-- with .app --

➜ clang --version
Apple clang version 17.0.0 (clang-1700.0.13.3)
Target: arm64-apple-darwin24.4.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

-- with default CommandLineTools version, also supported --

➜ clang --version
Apple clang version 17.0.0 (clang-1700.0.13.3)
Target: arm64-apple-darwin24.4.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

[greatgitsby]

i'll open panda and opendbc PRs with the context and we can get this issue fixed.