This new flag obtains the processor number on which a process is running.
Key parts of code and manual were borrowed from top.
This change was only inspired by PR129965 as I didn't think that the patch attached to it was correct. While choosing between ki_oncpu and ki_lastcpu is an improvement compared to that, my main disagreement with that patch whas the replacing of ki_estcpu with ki_lastcpu, which would render a part of the manual page definitely incorrect.
```
% ps -ocomm,cpu,cpu#,%cpu
COMMAND CPU C %CPU
tcsh 0 1 0.0
ps 0 0 0.0
tcsh 0 1 0.0
tcsh 0 0 0.0
make 0 1 0.0
make 0 0 0.0
sh 0 3 0.0
gmake 0 2 0.0
gmake 0 3 0.0
cc 0 1 0.0
cc 0 2 0.0
```