Fixed syntax issue between GCC and Clang/Visual Studio

Author: jwellbelove

include/etl/parameter_pack.h

@@ -134,17 +134,17 @@ namespace etl
   inline constexpr size_t parameter_pack_v = etl::parameter_pack<TTypes...>::template index_of_type<T>::value;
 #endif
 
-//#if ETL_USING_CPP17 && !ETL_USING_GCC_COMPILER
-//  //***********************************
-//  template <typename... TTypes>
-//  template <typename T>
-//  constexpr size_t parameter_pack<TTypes...>::template index_of_type<T>::value;
-//#else
+#if ETL_USING_CPP17 && !ETL_USING_GCC_COMPILER
+  //***********************************
+  template <typename... TTypes>
+  template <typename T>
+  constexpr size_t parameter_pack<TTypes...>::template index_of_type<T>::value;
+#else
   //***********************************
   template <typename... TTypes>
   template <typename T>
   constexpr size_t parameter_pack<TTypes...>::index_of_type<T>::value;
-//#endif
-}
 #endif
+}
 #endif
+#endif

support/Release notes.txt

@@ -14,6 +14,7 @@ Fixes:
 #956 Fix build error (etl::circular_buffer)
 #957 Support heterogenous lookup for maps
 #959 Treat bitset with size_type
+#972 template not allowed warning in parameter pack
 
 Pull Requests:
 #947 Remove unused git submodule config