Fixed some issues found by winapi_check.

dlls/winmm/mmsystem.c

@@ -5321,3 +5321,12 @@ void WINAPI WMMMidiRunOnce16(void)
 {
 	FIXME("(), stub!\n");
 }
+
+/**************************************************************************
+ * 			OutputDebugStr	 	[MMSYSTEM.30]
+ */
+void WINAPI OutputDebugStr16(
+    LPCSTR str) /* [in] The message to be logged and given to the debugger. */
+{
+    OutputDebugStringA( str );
+}

dlls/winmm/mmsystem.spec

@@ -8,7 +8,7 @@ owner	winmm
 5      pascal  mmsystemGetVersion() mmsystemGetVersion16
 6      pascal  DriverProc(long word word long long) DriverProc16
 8      pascal  WMMMIDIRUNONCE() WMMMidiRunOnce16
-30     pascal16 OutputDebugStr(str) OutputDebugStringA
+30     pascal16 OutputDebugStr(str) OutputDebugStr16
 31     pascal  DriverCallback(long word word word long long long) DriverCallback16
 32     pascal  StackEnter() StackEnter16
 33     pascal  StackLeave() StackLeave16