Move wxEventLoopManual::m_shouldExit to wxEventLoopBase.

No real changes, just make this flag available to the other event loop
implementations as they will need it soon.

See #10258.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74332 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/core/evtloop.h

@@ -80,9 +80,6 @@ protected:
     virtual void OSXDoRun();
     virtual void OSXDoStop();
 
-    // should we exit the loop?
-    bool m_shouldExit;
-
     // the loop exit code
     int m_exitcode;