Add missing dyn for cloudabi, redox, unix and wasm

src/libstd/sys/unix/thread.rs

@@ -49,7 +49,7 @@ unsafe fn pthread_attr_setstacksize(_attr: *mut libc::pthread_attr_t,
 }
 
 impl Thread {
-    pub unsafe fn new<'a>(stack: usize, p: Box<FnBox() + 'a>)
+    pub unsafe fn new<'a>(stack: usize, p: Box<dyn FnBox() + 'a>)
                           -> io::Result<Thread> {
         let p = box p;
         let mut native: libc::pthread_t = mem::zeroed();