[llvm] [X86][WinEH] Avoid stale RSP after Win64 dynalloca invokes (PR #191616)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

LGTM, but I'd like a second reviewer to look at this since it's a pretty deep change to the way stack allocation works.

https://github.com/llvm/llvm-project/pull/191616