libpmcstat scans the image (executable or library) for symbol tables in
order to be able to symbolicate callgraphs. However, we strip objects by
default, relying on separate debug files in /usr/lib/debug to provide
full symbol information to debuggers, and libpmcstat does not scan these
currently (though pmcstat itself does for other purposes). Thus, fix
this deficiency by also scanning a corresponding debug file, should it
exist, for symbols. This makes system-wide profiling of base much more
useful.
MFC after: 1 month