To get NGROUPS_MAX definition, we have to include sys/param.h,
including sys/types.h only is not enough.
The setgroups(2) manual page already advice including sys/param.h.

Index: lib/libc/sys/getgroups.2
===================================================================
--- lib/libc/sys/getgroups.2	(wersja 208452)
+++ lib/libc/sys/getgroups.2	(kopia robocza)
@@ -37,7 +37,7 @@
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
-.In sys/types.h
+.In sys/param.h
 .In unistd.h
 .Ft int
 .Fn getgroups "int gidsetlen" "gid_t *gidset"