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

[Jeremy Morse via llvm-commits]

jmorse wrote:

Looks like this is a proper problem when there's no body to a function (not something I'd considered possible) -- I'll add a filter to `emitInitialLocDirective` once it's tested.

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