Block type pack indexing on NVCC (#2563)

* Block type indexing if the compiler is NVCC.

Co-authored-by: Michael Schellenberger Costa <[email protected]>

libcudacxx/include/cuda/std/__type_traits/type_list.h

@@ -258,14 +258,19 @@ struct _CCCL_TYPE_VISIBILITY_DEFAULT __type_defer
 {};
 
 // Implementation for indexing into a list of types:
-#  if defined(__cpp_pack_indexing)
+#  if defined(__cpp_pack_indexing) && !defined(_CCCL_CUDA_COMPILER_NVCC)
+
+_CCCL_DIAG_PUSH
+_CCCL_DIAG_SUPPRESS_CLANG("-Wc++26-extensions")
 
 template <size_t _Ip, class... _Ts>
 using __type_index_c = _Ts...[_Ip];
 
 template <class _Ip, class... _Ts>
 using __type_index = _Ts...[_Ip::value];
 
+_CCCL_DIAG_POP
+
 // Versions of nvcc prior to 12.0 have trouble with pack expansion into
 // __type_pack_element in an alias template, so we use the fall-back
 // implementation instead.