Move wx/evtloopsrc.h to BASE_CMN_HDR from GUI_CMN_HDR

This header ends up being included by wx/apptrait.h, which is in
BASE_CMN_HDR, so it needs itself to be there too in order for
compilation to work when using non-GUI library build.

Closes #18038.

build/files

@@ -526,6 +526,7 @@ BASE_CMN_HDR =
     wx/event.h
     wx/eventfilter.h
     wx/evtloop.h
+    wx/evtloopsrc.h
     wx/except.h
     wx/features.h
     wx/flags.h
@@ -1021,7 +1022,6 @@ GUI_CMN_HDR =
     wx/docmdi.h
     wx/docview.h
     wx/effects.h
-    wx/evtloopsrc.h
     wx/fdrepdlg.h
     wx/filectrl.h
     wx/filehistory.h