wrong logic in .../source3/lib/system.c when checking for HAVE_SETGROUPS.
Patch:

diff -u ./source3/lib/system.c.orig ./source3/lib/system.c
--- ./source3/lib/system.c.orig	2010-05-17 06:51:23.000000000 -0500
+++ ./source3/lib/system.c	2010-05-27 07:13:48.000000000 -0500
@@ -1201,17 +1205,15 @@
 
 int sys_setgroups(gid_t UNUSED(primary_gid), int setlen, gid_t *gidset)
 {
-#if !defined(HAVE_SETGROUPS)
-	errno = ENOSYS;
-	return -1;
-#endif /* HAVE_SETGROUPS */
-
 #if defined(USE_BSD_SETGROUPS)
 	return sys_bsd_setgroups(primary_gid, setlen, gidset);
 #elif defined(HAVE_BROKEN_GETGROUPS)
 	return sys_broken_setgroups(setlen, gidset);
-#else
+#elif defined(HAVE_SETGROUPS)
 	return setgroups(setlen, gidset);
+#else
+	errno = ENOSYS;
+	return -1;
 #endif
 }
 

There's a releated but very old and closed report, #545.

Bye, Jojo