Define struct flock64 for riscv64-linux-gnu

src/unix/linux_like/linux/gnu/b64/riscv64/mod.rs

@@ -205,6 +205,14 @@ s! {
         pub l_len: ::off_t,
         pub l_pid: ::pid_t,
     }
+
+    pub struct flock64 {
+        pub l_type: ::c_short,
+        pub l_whence: ::c_short,
+        pub l_start: ::off64_t,
+        pub l_len: ::off64_t,
+        pub l_pid: ::pid_t,
+    }
 }
 
 pub const POSIX_FADV_DONTNEED: ::c_int = 4;