Add return statements to avoid gcc warnings.

dlls/ntdll/threadpool.c

@@ -258,6 +258,7 @@ static DWORD CALLBACK iocp_poller(LPVOID Arg)
             callback( err, transferred, overlapped );
         }
     }
+    return 0;
 }
 
 /***********************************************************************

dlls/winedos/vga.c

@@ -295,6 +295,7 @@ static void CALLBACK set_timer_rate( ULONG_PTR arg )
 static DWORD CALLBACK VGA_TimerThread( void *dummy )
 {
     for (;;) SleepEx( INFINITE, TRUE );
+    return 0;
 }
 
 static void VGA_DeinstallTimer(void)

dlls/winedos/vxd.c

@@ -407,6 +407,8 @@ static DWORD CALLBACK timer_thread( void *arg )
         *system_time = GetTickCount();
         Sleep( 55 );
     }
+
+    return 0;
 }
 
 

dlls/wineoss.drv/audio.c

@@ -1923,6 +1923,8 @@ static	DWORD	CALLBACK	wodPlayer(LPVOID pmt)
 	    dwNextFeedTime = dwNextNotifyTime = INFINITE;
 	}
     }
+
+    return 0;
 }
 
 /**************************************************************************