AK: Fix Clang 16 UBSan issue with zero-length Array

The current implementation of `Array<T, 0>` has a zero-length C array as
its storage type. While this is accepted as a GNU extension, when
compiling with Clang 16, an UBSan error is raised every time an object
is accessed whose only field is a zero-length array.

This is likely a bug in Clang 16's implementation of UBSan, which has
been reported here: llvm/llvm-project#61775

AK/Array.h

@@ -13,6 +13,16 @@
 
 namespace AK {
 
+namespace Detail {
+// This type serves as the storage of 0-sized `AK::Array`s. While zero-length `T[0]`
+// is accepted as a GNU extension, it causes problems with UBSan in Clang 16.
+template<typename T>
+struct EmptyArrayStorage {
+ T& operator[](size_t) const { VERIFY_NOT_REACHED(); }
+ constexpr operator T*() const { return nullptr; }
+};
+}
+
 template<typename T, size_t Size>
 struct Array {
  using ValueType = T;
@@ -109,7 +119,7 @@ struct Array {
  return value;
  }
 
- T __data[Size];
+ Conditional<Size == 0, Detail::EmptyArrayStorage<T>, T[Size]> __data;
 };
 
 template<typename T, typename... Types>