Silence two unused result warnings

c++/src/capnp/fuzz-test.c++

@@ -36,7 +36,7 @@ struct SkipTestHack {
   SkipTestHack() {
     if (getenv("CAPNP_SKIP_FUZZ_TEST") != nullptr) {
       char message[] = "Skipping test because CAPNP_SKIP_FUZZ_TEST is set in environment.\n";
-      write(STDOUT_FILENO, message, sizeof(message));
+      KJ_SYSCALL(write(STDOUT_FILENO, message, sizeof(message)));
       _exit(0);
     }
   }

c++/src/kj/io-test.c++

@@ -56,7 +56,7 @@ TEST(Io, WriteVec) {
 
 KJ_TEST("stringify AutoCloseFd") {
   int fds[2];
-  miniposix::pipe(fds);
+  KJ_SYSCALL(miniposix::pipe(fds));
   AutoCloseFd in(fds[0]), out(fds[1]);
 
   KJ_EXPECT(kj::str(in) == kj::str(fds[0]), in, fds[0]);