[llvm] [RISCV] Add TuneJumpIsExpensive (PR #191374)

[Sam Elliott via llvm-commits]

lenary wrote:

> > > What is the advantage of a tuning flag given that we already have `-mllvm -jump-is-expensive`?
> 
> > 
> 
> > using `-mllvm <whatever>` flags does not interact well with LTO, it would be better to have this as a feature or some other kind of attribute.
> 
> 
> 
> For LTO, we can pass options via `clang -flto -Wl,-mllvm,-<llvm-backend-option> ...`.

This applies the setting to the whole link, with a feature it can be on a per-function/per-file basis, even during linking.

https://github.com/llvm/llvm-project/pull/191374