[SYCL] Accessor tags, CTAD and host_accessor

sycl/include/CL/sycl/access/access.hpp

@@ -47,7 +47,28 @@ enum class address_space : int {
   local_space
 };
 
-}  // namespace access
+} // namespace access
+
+using access::target;
+using access_mode = access::mode;
+
+#if __cplusplus > 201402L
+
+template <access_mode mode> struct mode_tag_t {
+  explicit mode_tag_t() = default;
+};
+
+template <access_mode mode, target trgt> struct mode_target_tag_t {
+  explicit mode_target_tag_t() = default;
+};
+
+inline constexpr mode_tag_t<access_mode::read> read_only{};
+inline constexpr mode_tag_t<access_mode::read_write> read_write{};
+inline constexpr mode_tag_t<access_mode::write> write_only{};
+inline constexpr mode_target_tag_t<access_mode::read, target::constant_buffer>
+    read_constant{};
+
+#endif
 
 namespace detail {