[llvm] [AArch64] Only clear kill flags if necessary when merging str (PR #69680)

[Zhaoxuan Jiang via llvm-commits]

nocchijiang wrote:

I don't have commit access and I am trying to find some reviewers who reviewed/approved similar patches in the history. Sorry if this ping bothers you.

@davemgreen @fhahn

Blaming the lines leads me to @MatzeB who I believe is the original author to clear the kill flags. Please also take a look at this when you are free, thanks.

https://github.com/llvm/llvm-project/pull/69680