Reconcile HAVE_VARIADIC_MACROS and wxHAS_VARIADIC_MACROS definitions.

The main user-visible effect of this change is that giving configure
--disable-vararg-macros argument now really disables the use of variadic
macros whereas it didn't disable them in wx/cpp.h before.

It is, of course, also less confusing to not have two very similar but
different symbols.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74489 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

tests/controls/dialogtest.cpp

@@ -15,7 +15,7 @@
 
 #include "wx/testing.h"
 
-#ifdef wxHAS_VARIADIC_MACROS
+#ifdef HAVE_VARIADIC_MACROS
 
 #include "wx/msgdlg.h"
 #include "wx/filedlg.h"
@@ -122,4 +122,4 @@ void ModalDialogsTestCase::CustomDialog()
     CPPUNIT_ASSERT_EQUAL( 42, dlg.m_value );
 }
 
-#endif // wxHAS_VARIADIC_MACROS
+#endif // HAVE_VARIADIC_MACROS