[llvm] Try to use non-volatile registers for `preserve_none` parameters (PR #88333)

[Brandt Bucher via llvm-commits]

brandtbucher wrote:

@weiguozhi, @david-xl: Any chance you could review this small change? I think it'd be better to make it sooner rather than later, since it would be an ABI break once LLVM 19 ships.

(Sorry for the ping, I don't have permission to add reviewers.)

https://github.com/llvm/llvm-project/pull/88333