Make Qt::Initialization a C++11 class enum

And declare Qt::Uninitialized to be the same value because we're not
interested in the scoping rules of C++11 class enums. We're only
interested in avoiding the cast from Qt::Uninitialized to an integer.
That is to avoid the mistaken:

    QVector<Custom> vector(5, Qt::Uninitialized);

which is actually implicitly:

    QVector<Custom> vector(5, Custom(Qt::Uninitialized));

and likely not what the developer wanted.

Change-Id: I27eaacb532114dd188c4ffff13d374eb698bfbab
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/corelib/global/qnamespace.h

@@ -1536,9 +1536,16 @@ public:
         TitleBarArea    // For move
     };
 
+#if defined(Q_COMPILER_CLASS_ENUM) && defined(Q_COMPILER_CONSTEXPR)
+    enum class Initialization {
+        Uninitialized
+    };
+    static constexpr Q_DECL_UNUSED Initialization Uninitialized = Initialization::Uninitialized;
+#else
     enum Initialization {
         Uninitialized
     };
+#endif
 
     enum CoordinateSystem {
         DeviceCoordinates,