[llvm] [symbolizer] Empty string is not an error (PR #92660)

[Serge Pavlov via llvm-commits]

spavloff wrote:

> Blank lines get echoed? Yeah, I'm OK enough with it.

This patch implements a bit different solution: llvm-symbolizer reacts on blank line as on unknown symbol, - it prints `??:0`. Echoing blank lines also were discussed. The concern was the empty output, it would be more convenient to echo something visible, this is why the `ECHO` command was considered. Printing `??:0` also compatible with addr2line, but this is not too important, as the reaction on blank line could be implemented differently in compatibility mode.


https://github.com/llvm/llvm-project/pull/92660