[llvm] [DWARF] Emit a worst-case prologue_end flag for pathological inputs (PR #107849)

[Jeremy Morse via llvm-commits]

jmorse wrote:

(Taking a stab at usernames) CC @tedwoodward from the conference, I believe I mentioned this patch as a revising-the-placement-of-prologue_end thing that was coming along

https://github.com/llvm/llvm-project/pull/107849