This is necessary to ensure that wxUSE_EVENTLOOP_SOURCE which wraps the entire contents of this header is defined if it's included directly and not after already including wx/evtloop.h. See #10258. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74345 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775