Add a case for unknown arch (#5111)

Signed-off-by: Whitney Tsang <[email protected]>

Author: whitneywhtsang

third_party/intel/backend/arch_parser.c

@@ -51,6 +51,9 @@ extern "C" EXPORT_FUNC const char *parse_device_arch(uint64_t dev_arch) {
     arch = "ptl_u";
     break;
 #endif
+  case sycl::ext::oneapi::experimental::architecture::unknown:
+    std::cerr << "unknown sycl_arch" << std::endl;
+    break;
   default:
     std::cerr << "sycl_arch not recognized: " << (uint64_t)sycl_arch
               << std::endl;