how to list supplementary groups?

[Adrian Buciuman]

Hi,

Does GNU coreutils include any tool to list supplementary group IDs of
the running processes (or an error if the OS doesn't support
supplementary groups in the kernel) ?

I can't find anything about this either in the documentation of
coreutils, nor in the documentation of ps, nor in POSIX. So maybe I'm
missing something obvious.

Thank you