apple-clang failed again, forcing class instead of struct

include/gsl/span

@@ -68,11 +68,11 @@ namespace std
 // array is only used for a few constructors, so pulling the entire header is unnecessary for span.
 // The end user's logic will pull in the actual definition of array if they need it.
 template <class Type, std::size_t Sz>
-#if defined(__clang__) || defined(__APPLE__)
+#if defined(__clang__) && !defined(__APPLE__)
 struct array;
 #else
 class array;
-#endif // defined(__clang__) || defined(__APPLE__)
+#endif // defined(__clang__) && !defined(__APPLE__)
 }
 
 namespace gsl