[llvm] [llvm][stackmaps] Include prestine registers for liveness computation. (PR #90529)

[Juergen Ributzka via llvm-commits]

ributzka wrote:

That is how Webkit worked around the issue when it still used LLVM for the JIT. The JIT had to spill all the callee-saved registers (if they were used) because stackmaps didn't report any callee-saved registers.

https://github.com/llvm/llvm-project/pull/90529