[llvm] [MC] [Win64EH] Produce packed unwind for the special case of X19+LR (PR #169697)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

CC @pmsjt @LouisLaf

This goes on top of #169676. This is a requirement for making the case in #169588 packed - I guess I got nerd sniped into implementing this part after all, for completeness. :-) But I won't try to adjust the prologue code generation to hit this.


https://github.com/llvm/llvm-project/pull/169697