QMLDesigner: Replace compile-time check with run-time version.

We try to compile as much code as possible on all platforms, and that
particular piece does not have platform-specific compile-time
dependencies.

Change-Id: Ic78e6bdef24df6a7463f49979cdd8e2b8611c1b7
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

src/plugins/qmldesigner/designercore/instances/nodeinstanceserverproxy.cpp

@@ -80,12 +80,10 @@
 namespace {
 static QLatin1String qmlPuppetApplicationDirectoryForTests()
 {
-#ifdef Q_OS_WIN
-    //one more - debug/release dir
-    return QLatin1String("/../../../../../../bin/");
-#else
+    if (Utils::HostOsInfo::isWindowsHost())
+        //one more - debug/release dir
+        return QLatin1String("/../../../../../../bin/");
     return QLatin1String("/../../../../../bin/");
-#endif
 }
 } //namespace