[asan_symbolize] Avoid blocking when llvm-symbolizer is installed as addr2line

Summary:
Currently, llvm-symbolizer will print -1 when presented with -1 and not
print a second line. In that case we will block for ever trying to read
the file name. This also happens for non-existent files, in which case GNU
addr2line exits immediate, but llvm-symbolizer does not (see
https://llvm.org/PR42754). While touching these lines, I also added some
more debug logging to help diagnose this and potential future issues.

Reviewers: kcc, eugenis, glider, samsonov

Reviewed By: eugenis

Subscribers: kubamracek, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D65322

llvm-svn: 369924