[llvm] [MC,CodeGen] Update .prefalign for symbol-based preferred alignment (PR #184032)

[Nikita Popov via llvm-commits]

nikic wrote:

If https://llvm-compile-time-tracker.com/compare.php?from=dddd06be8c3ed10eaef4f986ec4ceb828be7e789&to=f42b3383765cfaeea7a0654995bb6939278325f4&stat=instructions:u is the compile-time tracker run corresponding to this change, it looks like this is causing massive regressions at `-O0 -g`.

https://github.com/llvm/llvm-project/pull/184032