Binary distros often contain the symbols in a file, making crashes debuggable at least a little bit. Right now, unless you build mysql with debugging and no stripping, this is impossible. See: http://dev.mysql.com/doc/internals/en/using-stack-trace.html Reproducible: Always
BTW, I understand that one can enable saving of debug information, but that doesn't really do much good if you run into a bug after you built the app. Then you have to rebuild and schizophrenically hope to hit it again.
You probably want FEATURES="splitdebug"