seccomp: beef up @process group a bit

Include the waid syscalls. If we permit forking then we should also
permit waiting for a process.

Similar to that: also permit determining the usage counters for
processes.

Include calls to determine process/thread identity. They have little
impact security-wise, but are very likely used when process management
of any form is done.

Also, add rt_sigqueueinfo + rt_tgsigqueueinfo as they are similar to
kill() and friends, but permit passing along a userdata ptr.