check for wxUSE_TIMER in headers, not the files including them

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@47323 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/unix/private/timer.h

@@ -11,6 +11,8 @@
 #ifndef _WX_UNIX_PRIVATE_TIMER_H_
 #define _WX_UNIX_PRIVATE_TIMER_H_
 
+#if wxUSE_TIMER
+
 #include "wx/private/timer.h"
 
 // the type used for milliseconds is large enough for microseconds too but
@@ -135,4 +137,6 @@ private:
 // returns the number of microseconds since the Epoch
 extern wxUsecClock_t wxGetLocalTimeUsec();
 
+#endif // wxUSE_TIMER
+
 #endif // _WX_UNIX_PRIVATE_TIMER_H_