Implement `Sync` for some windows sys types

src/libstd/sys/windows/mutex.rs

@@ -22,6 +22,8 @@ pub struct Mutex { inner: atomic::AtomicUint }
 
 pub const MUTEX_INIT: Mutex = Mutex { inner: atomic::INIT_ATOMIC_UINT };
 
+unsafe impl Sync for Mutex {}
+
 #[inline]
 pub unsafe fn raw(m: &Mutex) -> ffi::LPCRITICAL_SECTION {
     m.get()

src/libstd/sys/windows/pipe.rs

@@ -559,6 +559,8 @@ pub struct UnixListener {
     name: CString,
 }
 
+unsafe impl Sync for UnixListener {}
+
 impl UnixListener {
     pub fn bind(addr: &CString) -> IoResult<UnixListener> {
         // Although we technically don't need the pipe until much later, we
@@ -603,11 +605,15 @@ pub struct UnixAcceptor {
     deadline: u64,
 }
 
+unsafe impl Sync for UnixAcceptor {}
+
 struct AcceptorState {
     abort: Event,
     closed: atomic::AtomicBool,
 }
 
+unsafe impl Sync for AcceptorState {}
+
 impl UnixAcceptor {
     pub fn accept(&mut self) -> IoResult<UnixStream> {
         // This function has some funky implementation details when working with