[llvm-symbolizer] Add support for specifying addresses on command-line
GNU addr2line accepts input addresses both on the command-line and via
stdin. llvm-symbolizer previously only supported the latter. This
change adds support for the former. As with addr2line, the new
behaviour is to only look for addresses on stdin if no positional
arguments were provided to llvm-symbolizer.
Reviewed by: ruiu
Differential Revision: https://reviews.llvm.org/D56272