sync: make new_mutex() and new_waitgroup() return &Mutex and &Waitgroup

vlib/sync/sync_nix.v

@@ -16,9 +16,8 @@ pub struct Mutex {
 	mutex C.pthread_mutex_t
 }
 
-pub fn new_mutex() Mutex {
-	m := Mutex{
-	}
+pub fn new_mutex() &Mutex {
+	m := &Mutex{}
 	C.pthread_mutex_init(&m.mutex, C.NULL)
 	return m
 }

vlib/sync/sync_windows.v

@@ -39,8 +39,8 @@ const (
 	WAIT_FAILED        = 0xFFFFFFFF
 )
 
-pub fn new_mutex() Mutex {
-	sm := Mutex{}
+pub fn new_mutex() &Mutex {
+	sm := &Mutex{}
 	unsafe {
 		mut m := sm		
 		m.mx = C.CreateMutex(0, false, 0)
@@ -48,8 +48,8 @@ pub fn new_mutex() Mutex {
 			m.state = .broken // handle broken and mutex state are broken
 			return sm
 		}		
-		return sm
 	}
+	return sm
 }
 
 pub fn (m mut Mutex) lock() {

vlib/sync/waitgroup.v

@@ -5,15 +5,12 @@ module sync
 // [init_with=new_waitgroup] // TODO: implement support for init_with struct attribute, and disallow WaitGroup{} from outside the sync.new_waitgroup() function.
 pub struct WaitGroup {
 mut:
-	mu     Mutex
+	mu     &Mutex = &Mutex(0)
 	active int
 }
 
-pub fn new_waitgroup() WaitGroup {
-	mut w := WaitGroup{
-	}
-	w.mu = sync.new_mutex()
-	return w
+pub fn new_waitgroup() &WaitGroup {
+	return &WaitGroup{mu: sync.new_mutex() }
 }
 
 pub fn (wg mut WaitGroup) add(delta int) {