[clang] [llvm] Disable pre-link LTO vectorisation and loop unroll for at O2 and O3 optimisation levels (PR #195886)

[Luke Lau via cfe-commits]

https://github.com/lukel97 requested changes to this pull request.

Really sorry for the request changes but marking to make explicit the RISC-V regressions that need addressed. Will try to unblock ASAP

https://github.com/llvm/llvm-project/pull/195886