Add O_NOFOLLOW flag

src/flag.rs

@@ -45,6 +45,7 @@ pub const O_EXCL: usize =       0x0800_0000;
 pub const O_DIRECTORY: usize =  0x1000_0000;
 pub const O_STAT: usize =       0x2000_0000;
 pub const O_SYMLINK: usize =    0x4000_0000;
+pub const O_NOFOLLOW: usize =   0x8000_0000;
 pub const O_ACCMODE: usize =    O_RDONLY | O_WRONLY | O_RDWR;
 
 pub const SEEK_SET: usize = 0;