Fix 'qt4test' test executable when only Qt4 is present

This always tries to load a 'qt5core_fr' translation file, when it is
actually named 'qtNcore_fr'(where N is the qt version).

test cases/frameworks/4 qt/meson.build

@@ -83,6 +83,7 @@ foreach qt : ['qt4', 'qt5']
     qtcore = dependency(qt, modules : 'Core', method : get_option('method'))
 
     qtcoreapp = executable(qt + 'core', 'q5core.cpp',
+      cpp_args: '-DQT="@0@"'.format(qt),
       dependencies : qtcore)
 
     test(qt + 'test', qtcoreapp)

test cases/frameworks/4 qt/q5core.cpp

@@ -15,7 +15,7 @@ int main(int argc, char **argv) {
   app.installTranslator(&qtTranslator);
 
   QTranslator myappTranslator;
-  if(!myappTranslator.load("qt5core_fr") )
+  if(!myappTranslator.load(QT "core_fr") )
     return 1;
 
   app.installTranslator(&myappTranslator);