[llvm] [InitUndef] Enable the InitUndef pass on all targets (PR #108353)

[Nikita Popov via llvm-commits]

nikic wrote:

I've updated the PR to restore the hook and only enable it on AArch64 additionally. I've renamed the hook to make it clearer when you are supposed to enable it.

Though I'm wondering if it wouldn't be better to enable it by default and only disable on AMDGPU, as that is the conservatively correct behavior, and it doesn't seem like this affects register allocation/scheduling on other targets anyway.

https://github.com/llvm/llvm-project/pull/108353