Enhance llvm-build behavior

[WangJialei-A]

Developers may synchronize the main branch with the PR branch by merging the main branch into the PR branch. This process might generate a commit that includes modifications to the llvm-version.txt file, which in turn could trigger the LLVM build CI.

Perhaps a better approach would be to hook the llvm-version.txt file only on the main branch.

[leshikus]

There is a problem regarding it, the developer wants their branch to work. If they changed the hash, llvm build has to be made to enable their branch to work.
There is a problem though. The developer has to restart CI on his branch manually once llvm build is completed

[WangJialei-A]

There is a problem regarding it, the developer wants their branch to work. If they changed the hash, llvm build has to be made to enable their branch to work. There is a problem though. The developer has to restart CI on his branch manually once llvm build is completed

I think a better practice is to use a separate PR for updating the LLVM version, rather than mixing it with other development work.

If someone updates the LLVM version on the main branch, I believe it is completely acceptable for the CI results of a PR to fail. This failure serves as a reminder to developers that the LLVM version used in their PR is outdated.

[leshikus]

@WangJialei-A I agree