[clang] [clang] Move opt level in clang toolchain to clang::ConstructJob start (PR #141036)

[Omar Ahmed via cfe-commits]

omarahmed1111 wrote:

@tarunprabhu @florianhumblot @alexey-bataev @RKSimon @phoebewang Not sure who to as for review, so please review or if you could mention who is responsible for reviewing this code, Thanks!

https://github.com/llvm/llvm-project/pull/141036