[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 commented:

Unfortunately the SLP regression on imagick_r still exists on RISC-V, is it ok if we hold off on landing this until that is fixed?

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