QV4::Heap::SharedArrayBuffer: avoid std::aligned_storage (deprecated …

…in C++23)

... by rolling our own.

Qt 5.15 uses a pointer (additional indirection), not aligned_storage,
so isn't affected.

References:
- cplusplus/papers#197
- https://wg21.link/p1413

Pick-to: 6.4 6.2
Task-number: QTBUG-99122
Change-Id: Ia116dc11336901a19fc227fb68ac266c1bfbbcb1
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/qml/jsruntime/qv4arraybuffer_p.h

@@ -60,7 +60,10 @@ struct Q_QML_PRIVATE_EXPORT SharedArrayBuffer : Object {
         return *reinterpret_cast<QArrayDataPointer<char> *>(&arrayDataPointerStorage);
     }
 
-    std::aligned_storage_t<sizeof(QArrayDataPointer<char>), alignof(QArrayDataPointer<char>)>
+    template <typename T>
+    struct storage_t { alignas(T) unsigned char data[sizeof(T)]; };
+
+    storage_t<QArrayDataPointer<char>>
     arrayDataPointerStorage;
     bool isShared;
 };