[llvm] [premerge] Route macOS build through a monolithic script to enable Job Summary (PR #211565)

[Arseniy Obolenskiy via llvm-commits]

aobolensk wrote:

> Overall direction looks good, however the `.ci/utils.sh` will need to be configured to work on macOS.

It seems no other changes are required to enable utils.sh on macOS 

https://github.com/llvm/llvm-project/pull/211565