use clang 13

[lmb]

clang 13 has been out for a while and is now available on apt.llvm.org. Switch testdata, etc. to the new version. We still need clang-9 on CI since bpf2go tests rely on it.

[ti-mo]

Since we have the llvm (and Go) builder image now, could we consider running the bpf2go tests containerized on CI? I can't get a working clang9 build on Arch anymore since a few weeks now (my libffi is too new) and not sure if this will be fixed. As a result, I have to skip the bpf2go tests for now locally.

[lmb]

Yeah we can consider doing that. The downside is that builds will probably take longer due to the 500MiB container image we need to pull. Maybe a good middle ground is to add another makefile target to use the container but not use that on CI yet? Your local workflow could be make test. Either way, can we tackle that in a separate PR?

[ti-mo]

My problem is mostly that go test is currently broken on my machine. Couldn't we use the clang binary in the Go test suite (should point to something on CI, right?) and a fixed version in the Makefile, since that runs containerized and its output needs to be stable?

[lmb]

That's why I added 76957b9 to explain why we require clang-9. It's not called by the Makefile (unfortunately, since that already runs in the container).

Some options: skip the tests if clang-9 is missing (kinda suboptimal); use an env var to override the version we test against (less meh, also not great); bump the minimum version and hope we don't introduce incompatibilities.

Do you mind if we merge this PR though? I need clang-13 for some bpf2go stuff.