Explicitly document wxMessageOutputFlags.

They were already mentioned in wxMessageOutputBest ctor documentation but now
add the standalone enum too to make the documentation header semantically valid.

Closes #14082.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70866 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/msgout.h

@@ -113,6 +113,17 @@ public:
     wxMessageOutputStderr(FILE *fp = stderr);
 };
 
+/**
+    Flags used with wxMessageOutputBest.
+
+    See wxMessageOutputBest::wxMessageOutputBest().
+ */
+enum wxMessageOutputFlags
+{
+    wxMSGOUT_PREFER_STDERR = 0, ///< use stderr if available (this is the default)
+    wxMSGOUT_PREFER_MSGBOX = 1  ///< always use message box if available
+};
+
 /**
     Output messages in the best possible way.