Fix linking when wxUSE_VALIDATORS==0

The changes from 25e9be6873 don't work, at least with GCC 9, as the compiler
seems to be removing the definition of the wxDefaultValidator variable.

include/wx/validate.h

@@ -99,19 +99,19 @@ private:
 
 #define wxVALIDATOR_PARAM(val) val
 
+extern WXDLLIMPEXP_DATA_CORE(const wxValidator) wxDefaultValidator;
+
 #else // !wxUSE_VALIDATORS
     // wxWidgets is compiled without support for wxValidator, but we still
     // want to be able to pass wxDefaultValidator to the functions which take
     // a wxValidator parameter to avoid using "#if wxUSE_VALIDATORS"
     // everywhere
-    class WXDLLIMPEXP_FWD_CORE wxValidator;
+    class wxValidator { };
+    #define wxDefaultValidator wxValidator()
 
     // this macro allows to avoid warnings about unused parameters when
     // wxUSE_VALIDATORS == 0
     #define wxVALIDATOR_PARAM(val)
 #endif // wxUSE_VALIDATORS/!wxUSE_VALIDATORS
 
-extern WXDLLIMPEXP_DATA_CORE(const wxValidator) wxDefaultValidator;
-
 #endif // _WX_VALIDATE_H_
-

src/common/validate.cpp

@@ -25,6 +25,8 @@
 
 wxIMPLEMENT_DYNAMIC_CLASS(wxValidator, wxEvtHandler);
 
+const wxValidator wxDefaultValidator;
+
 // VZ: personally, I think true would be more appropriate - these bells are
 //     _annoying_
 bool wxValidator::ms_isSilent = false;
@@ -37,10 +39,5 @@ wxValidator::wxValidator()
 wxValidator::~wxValidator()
 {
 }
-#else
-
-class WXDLLIMPEXP_CORE wxValidator { };
 
 #endif // wxUSE_VALIDATORS
-
-const wxValidator wxDefaultValidator;