Fixes for dereference operator.

src/Memory/BorrowedPtr.hpp

@@ -29,13 +29,10 @@ namespace ArbUt {
             AssertNotNull(_raw);
             return _raw;
         }
-        inline T operator*() const {
-            if constexpr (std::is_abstract<T>()) {
-                static_assert(!std::is_abstract<T>(), "You're not allowed to dereference an abstract class.");
-            } else {
-                AssertNotNull(_raw);
-                return *_raw;
-            }
+
+        inline typename std::enable_if<!std::is_abstract<T>::value, bool>::type operator*() const {
+            AssertNotNull(_raw);
+            return *_raw;
         }
 
         inline T* GetRaw() const noexcept { return _raw; }