[llvm] Symbolize line zero as if no source info is available (PR #124846)

[Reid Kleckner via llvm-commits]

rnk wrote:

I agree with everything you said, but where is this actually implemented in the LLVM source code? I looked hard at the MC DWARF line table encoding, but I couldn't find where this is implemented.

https://github.com/llvm/llvm-project/pull/124846