[llvm] [SPARC] Preserve liveins after leaf register remapping (PR #213359)

[Daniel Cederman via llvm-commits]

doac wrote:

Hi! I tried the patch and it fixes the problem, but I got a performance regression where a function that needed more than only the available %o registers was still treated as a leaf function, leading to register spills. I have attached a generated test that triggers this.
[leafproc-high-pressure.txt](https://github.com/user-attachments/files/31640942/leafproc-high-pressure.txt)


https://github.com/llvm/llvm-project/pull/213359