This commit adds the dup() function, which was omitted when sys_dup()
was defined.  This is a port of nolibc's upstream commit 
47cc42a79c92
to the Linux kernel.
Fixes: 66b6f755ad45 ("rcutorture: Import a copy of nolibc")
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com> [arm64]
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
        return ret;
 }
 
+static __attribute__((unused))
+int dup(int fd)
+{
+       int ret = sys_dup(fd);
+
+       if (ret < 0) {
+               SET_ERRNO(-ret);
+               ret = -1;
+       }
+       return ret;
+}
+
 static __attribute__((unused))
 int dup2(int old, int new)
 {