New buildbots to mimic Pull Request environment

I have added two new buildbots

  • premerge-monolithic-windows 271
  • premerge-monolithic-linux 272

that have the same setup as agents we use for Pull Request tests.
Hopefully that will give a heads up about new breakages to authors who didn’t waited for PR build to complete or committed without pull request. The situations when PR testing is broken by a broken main should happen less often.

Linux bot builds every commit individually, Windows can only hanlde bunch builds.

Initial discussion: Create a minimal CI that validates tree before merge · Issue #56674 · llvm/llvm-project · GitHub