[llvm] [Symbolize] Always use filename:line from debug info when debug info for the given address is available. (PR #128619)

[Reid Kleckner via llvm-commits]

rnk wrote:

> Feels a bit awkward to add new virtual functions for this - when, at least I think in theory, the new virtual functions are strictly more expressivse than the old ones (so, one option would be to rename the virtual functions to add the new behavior, then add non-virtual wrapping functions that provide the old behavior under the original name).
> 
> But, also - maybe this isn't the level at which to make the change? Perhaps inside the DILine Info, the file/line number should be wrapped in an optional, so it's clear that neither of those things is present/valid?

I share this concern, and I think there is already a lot of prior art for expressing ideas like "source" and "confidence level" inside of the DILineInfo struct. What is the meaning of the `IsApproximateLine` boolean, for example? We could freely add another boolean there to indicate our confidence, i.e. the presence of a line table. The callers that currently distinguish success by checking for line 0 would migrate to this boolean.

https://github.com/llvm/llvm-project/pull/128619