Auto merge of #504 - Idolf:tmpfile, r=alexcrichton

Add O_TMPFILE constant

Author: bors

src/unix/notbsd/mod.rs

@@ -253,6 +253,7 @@ pub const RUSAGE_SELF: ::c_int = 0;
 pub const O_RDONLY: ::c_int = 0;
 pub const O_WRONLY: ::c_int = 1;
 pub const O_RDWR: ::c_int = 2;
+pub const O_TMPFILE: ::c_int = 0o20000000 | O_DIRECTORY;
 
 pub const SOCK_CLOEXEC: ::c_int = O_CLOEXEC;