test: Don't use std::chrono_literals, fix building hello-exception in C++11 mode

std::chrono_literals require C++14.

This simplifies building hello-exception on macOS, where current
Apple Clang still default to C++11.

test/hello-exception.cpp

@@ -95,8 +95,7 @@ int main(int argc, char* argv[]) {
     recurse(10);
     if (do_wait) {
         fprintf(stderr, "Waiting\n");
-        using namespace std::chrono_literals;
-        std::this_thread::sleep_for(10s);
+        std::this_thread::sleep_for(std::chrono::seconds(10));
         fprintf(stderr, "Exiting\n");
     }
     return 0;