Merge branch 'sync_impl' into 'master'

sync implementation

See merge request redox-os/relibc!375

src/platform/redox/mod.rs

@@ -832,6 +832,10 @@ impl Pal for Sys {
         0
     }
 
+    fn sync() -> c_int {
+        0
+    }
+
     fn umask(mask: mode_t) -> mode_t {
         e(syscall::umask(mask as usize)) as mode_t
     }