perf: Propagate term signal to child

If we launch the child on behalf of the user, ensure that it dies
along with ourselves when we are interrupted.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
LKML-Reference: <1254616502-4728-1-git-send-email-chris@chris-wilson.co.uk>
Signed-off-by: Ingo Molnar <mingo@elte.hu>