If it is implemented - I am not sure it is - it has an fp prefix since a couple of versions, so fpsetpgrp..
[edit] it is implemented, but maybe not for all platforms. I found it at least in /rtl/netwlibc/libc.pp using grep.
I can't imagine you really want to use netware/nlm, btw. But that is the only one that matched: seems tied to netware libc, not C.