From: Daniel Jacobowitz <dan@debian.org>

Right now, CLONE_DETACHED threads silently vanish from GDB's sight when
they exit.  This patch lets the thread report its exit to the debugger, and
then be auto-reaped as soon as it is collected, instead of being reaped as
soon as it exits and not reported at all.

GDB works either way, but this is more correct and will be useful for some
later GDB patches.