Run LLVM 20 on ppc64

[NattyNarwhal]

Already installed, be consistent with the other platforms. Applying to PHP-8.2 and merging upward since this file needs to be consistent across branches.

[TimWolla]

since this file needs to be consistent across branches.

@iluuu1994 Does it actually for compiler versions? Also: I tried adding the PPC64 label and then reran the job, should it pick up the label then? It didn't, but not sure if that should work for reruns vs triggering a completely new job.

[iluuu1994]

Does it actually for compiler versions?

The file should be consistent across branches, but compiler versions shouldn't be bumped for old PHP versions. So this should be done via a version check, preferably in matrix.php via config option passed to the yml file as in the Ubuntu builds.

Also: I tried adding the PPC64 label and then reran the job, should it pick up the label then? It didn't, but not sure if that should work for reruns vs triggering a completely new job.

I think this is a GitHub Actions quirk where rerunning the job re-uses the previous metadata, including the old labels. See https://github.com/php/php-src/actions/runs/25443461773/job/74650931082?pr=21964, the labels are missing in the input.

[NattyNarwhal]

The file should be consistent across branches, but compiler versions shouldn't be bumped for old PHP versions. So this should be done via a version check, preferably in matrix.php via config option passed to the yml file as in the Ubuntu builds.

I noticed Alpine got bumped to clang-20 on PHP-8.2 too.

[iluuu1994]

To be more precise: It's ok to bump compiler versions in old branches in case the version goes out of support. But it's also useful to keep it to find compatibility issues. We also don't backport all fixes for warnings, at least to security branches. So that can also be an issue. But I'm not strictly against this.

Also: I tried adding the PPC64 label and then reran the job, should it pick up the label then? It didn't, but not sure if that should work for reruns vs triggering a completely new job.

Oh and also, PPC only runs on 8.4+, so we can't test it in this PR unfortunately.