Keep NIN_BALLOONxxx checks and definitions.

Apparently some gcc flavors (like g++ (GCC) 5.3.0 from AppVeyor) do not define these symbols. FWIW tdm-gcc-5.1.0 does not need them.

This partially reverts commit 299a06c86e.

src/msw/taskbar.cpp

@@ -33,6 +33,11 @@
 #include "wx/platinfo.h"
 #include "wx/msw/private.h"
 
+#ifndef NIN_BALLOONTIMEOUT
+    #define NIN_BALLOONTIMEOUT      0x0404
+    #define NIN_BALLOONUSERCLICK    0x0405
+#endif
+
 // initialized on demand
 static UINT gs_msgTaskbar = 0;
 static UINT gs_msgRestartTaskbar = 0;