Fetch host <utility> to populate tuple_size

include/cuda/std/tuple

@@ -10,6 +10,12 @@
 #ifndef _CUDA_TUPLE
 #define _CUDA_TUPLE
 
+#if !defined(__CUDACC_RTC__)
+// Fetch utility to get primary template for ::std::tuple_size necessary for the specialization of
+// ::std::tuple_size<cuda::std::tuple> to enable structured bindings. See https://github.com/NVIDIA/libcudacxx/issues/316 
+#include <utility>
+#endif
+
 #include "cstdint"
 #include "climits"
 
@@ -29,5 +35,3 @@
 #include "detail/__pragma_pop"
 
 #endif //_CUDA_TUPLE
-
-

include/cuda/std/utility

@@ -10,6 +10,11 @@
 #ifndef _CUDA_UTILITY
 #define _CUDA_UTILITY
 
+#if !defined(__CUDACC_RTC__)
+// Fetch utility to populate tuple_size
+#include <utility>
+#endif
+
 #include "type_traits"
 #include "version"
 
@@ -23,5 +28,3 @@
 #include "detail/__pragma_pop"
 
 #endif //_CUDA_UTILITY
-
-