Improvements for building minimal builds and new ports: wxUSE_* usage and minor cleaning.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39633 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/univ/scrtimer.h

@@ -14,6 +14,10 @@
 
 // NB: this class is implemented in scrolbar.cpp
 
+#include "wx/defs.h"
+
+#if wxUSE_TIMER
+
 #include "wx/timer.h"
 
 // ----------------------------------------------------------------------------
@@ -42,4 +46,6 @@ protected:
     bool m_skipNext;
 };
 
+#endif // wxUSE_TIMER
+
 #endif // _WX_UNIV_SCRTIMER_H