Use the same function for logging dynlib errors on all platforms

Reduces the amount of #ifdefs scattered all over the code, thereby
simplifying the code.

The function was renamed from Error() to ReportError() to emphasize what
its purpose is.

Error messages logged on *nix are now a bit more verbose, as they are
prefixed with our own description text, which were earlier omitted on
platforms using the dlxxx() API.

include/wx/dynlib.h

@@ -357,11 +357,9 @@ protected:
     // common part of GetSymbol() and HasSymbol()
     void* DoGetSymbol(const wxString& name, bool* success = NULL) const;
 
-#ifdef HAVE_DLERROR
-    // log the error after a dlxxx() function failure
-    static void Error();
-#endif // HAVE_DLERROR
-
+    // log the error after an OS dynamic library function failure
+    static void ReportError(const wxString& msg,
+                            const wxString& name = wxString());
 
     // the handle to DLL or NULL
     wxDllType m_handle;