[llvm] [clang] [Github] Use building LLVM as perf-training for CI container (PR #80713)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

Looks like there was a transient failure in the stage2 build while loading the container image. I've restarted it and everything seems to be going fine. Hopefully that's not an issue going forward.

https://github.com/llvm/llvm-project/pull/80713