[POWERPC] During VM oom condition, kill all threads in process group

[POWERPC] During VM oom condition, kill all threads in process group

We have had complaints where a threaded application is left in a bad state
after one of it's threads is killed when we hit a VM: out_of_memory
condition.

Killing just one of the process threads can leave the application in a
bad state, whereas killing the entire process group would allow for
the application to restart, or be otherwise handled, and makes it very
obvious that something has gone wrong.

This change allows the entire process group to be taken down, rather than
just the one thread.

lightly tested on powerpc

Signed-off-by: Will <will_schmidt@vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>