Declare getgrent/setgrent/endgrent as missing.

Bug: 19340053
Change-Id: I42bfeda95e6f262e2e74ab47336ea346c2de7e4a
diff --git a/libc/include/grp.h b/libc/include/grp.h
index fc4d520..ab90022 100644
--- a/libc/include/grp.h
+++ b/libc/include/grp.h
@@ -54,9 +54,9 @@
 struct group	*getgrgid(gid_t);
 struct group	*getgrnam(const char *);
 #if __POSIX_VISIBLE >= 200112 || __XPG_VISIBLE
-struct group	*getgrent(void);
-void		 setgrent(void);
-void		 endgrent(void);
+struct group	*getgrent(void) __errorattr("This function is meaningless on Android.");
+__errordecl(setgrent, "This function is meaningless on Android.");
+__errordecl(endgrent, "This function is meaningless on Android.");
 int		 getgrgid_r(gid_t, struct group *, char *,
 		    size_t, struct group **);
 int		 getgrnam_r(const char *, struct group *, char *,