csky: Fixup compile warning for three unimplemented syscalls

Implement fstat64, fstatat64, clone3 syscalls to fixup
checksyscalls.sh compile warnings.
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>

arch/csky/include/uapi/asm/unistd.h

 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
 // Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
 
+#define __ARCH_WANT_STAT64
+#define __ARCH_WANT_NEW_STAT
 #define __ARCH_WANT_SYS_CLONE
+#define __ARCH_WANT_SYS_CLONE3
 #define __ARCH_WANT_SET_GET_RLIMIT
 #define __ARCH_WANT_TIME32_SYSCALLS
 #include <asm-generic/unistd.h>