[llvm] [win][x64] Unwind v2 4/4: Use chaining to split unwind info if needed, and allow dealloc to be elided if setframe + frame pointer is used (PR #159206)

[Daniel Paoliello via llvm-commits]

dpaoliello wrote:

> Please add a test that emits the `.seh_splitchained` assembly directive.

Done. Also remembered that we changed the design of splitting to require ending the prolog, so added that and tests.



https://github.com/llvm/llvm-project/pull/159206