runtime/race: upstream OpenBSD support is removed

[cherrymui]

LLVM TSAN removed OpenBSD support ( https://reviews.llvm.org/rG53065c543fe3f1e7913c9e8f2487d76034afa249 )
What do we do for the race detector on OpenBSD? Do we want to remove it, or try to add it back to LLVM?

cc @dvyukov @4a6f656c @golang/runtime

[gopherbot]

Change https://go.dev/cl/397494 mentions this issue: runtime/race: update syso files to new TSAN runtime (v3)

[beoran]

Why was it even dropped? It is not very clear from the issue above.

[qbit]

I added the initial bits for llvm. No clue why they added it - I will ask.

My pref is to keep it enabled in Go if at all possible. I use the feature pretty regularly.

[randall77]

For now we can just not update TSAN on openbsd. The updates we want to do are mostly performance, so it is ok if it isn't available everywhere (the 8192 goroutine limit might be annoying if it is gone everywhere else, though).

Longer term that isn't a solution, though. At some point we'd have to either fix openbsd support or drop the openbsd race detector.

[dvyukov]

Honestly, I don't know what happened. But it was removed from everywhere, not just tsan.
It seems that the simplest option is not update OpenBSD runtime.