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

[Jeremy Morse via llvm-commits]

jmorse wrote:

For when I get back to this tomorrow -- is the intention of that test (artificial_location in TestSourceManager) specifically about stepping into prologues + the start of a function, or is it about stimulating LLDBs handling of line-zero locations? I can almost certainly cook up something that stops on line-zero somehow (currently thinking a crash).

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