Add MFD_ constants for memfd_create

Author: Bryant Mairs

libc-test/build.rs

@@ -248,6 +248,8 @@ fn main() {
         if !uclibc && !musl && !emscripten {
             cfg.header("linux/dccp.h");
         }
+
+        cfg.header("linux/memfd.h");
     }
 
     if linux {

src/unix/notbsd/mod.rs

@@ -803,6 +803,9 @@ pub const POLLNVAL: ::c_short = 0x20;
 pub const POLLRDNORM: ::c_short = 0x040;
 pub const POLLRDBAND: ::c_short = 0x080;
 
+pub const MFD_CLOEXEC: ::c_uint = 0x0001;
+pub const MFD_ALLOW_SEALING: ::c_uint = 0x0002;
+
 f! {
     pub fn FD_CLR(fd: ::c_int, set: *mut fd_set) -> () {
         let fd = fd as usize;