Portability problems not fixed by Gnulib:
@itemize
@item
+This function is unsafe to call between @code{fork} and @code{exec} if
+the parent process is multi-threaded. Instead, use @code{getgroups} or
+@code{getgrouplist} (or use the gnulib module @code{mgetgroups})
+before forking, and @code{setgroups} in the child.
+@item
This function is missing on some platforms:
mingw, MSVC 9, Interix 3.5, BeOS.
@end itemize