Enable the clone3 syscall for OpenRISC. We use the generic version. This was tested with the clone3 test from selftests. Note, for all tests to pass it required enabling CONFIG_NAMESPACES which is not enabled in the default OpenRISC kernel config. Signed-off-by: Stafford Horne <shorne@gmail.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com>