Patch for PR c/12373

[Giovanni Bajo]

Eric Botcazou wrote:

> You can't reasonably expect that a PR assigned to someone will be
> looked at by others.  This would defeat the whole purpose of
> assigning PRs.  This was either a bug triaging problem or Zack's
> problem.

Maybe we can have some machinery to automatically unassign/ping an assigned bug
if it doesn't get any update in a certain amount of time (say 2-3 months).
Either that, or Bugmasters can do that manually, checking PR by PR, in case
there are some specific exceptions. Would this help?

Giovanni Bajo