MINOR: tools: don't emit "+0" for symbol names which exactly match known ones

MINOR: tools: don't emit "+0" for symbol names which exactly match known ones

resolve_sym_name() knows a number of symbols, but when one exactly matches
(e.g. a task's handler), it systematically displays the offset behind it
("+0"). Let's only show the offset when non-zero. This can be backported
as this is helpful for debugging.