This only compiles with warnings for me:

stat_test.c: In function 'main':
stat_test.c:557:3: warning: 'sval' may be used uninitialized in this function [-Wmaybe-uninitialized]
   check(sval == scheck,
   ^
stat_test.c:451:20: note: 'sval' was declared here
  long long scheck, sval;
                    ^
stat_test.c:542:3: warning: 'uval' may be used uninitialized in this function [-Wmaybe-uninitialized]
   check(uval == ucheck,
   ^
stat_test.c:450:29: note: 'uval' was declared here
  unsigned long long ucheck, uval;
                             ^

And running it then fails for me on Debian stable:

--- tests/generic/420.out	2017-03-31 16:24:11.643845876 +0000
+++ /root/xfstests/results//generic/420.out.bad	2017-03-31 16:26:23.820512545 +0000

@@ -8,4 +8,10 @@
 20+0 records out
 Test statx on a symlink
 Test statx on an AF_UNIX socket
+nc: invalid option -- 'U'
+/bin/nc: invalid option -- 'U'
+nc -h for helpnc -h for help
+
+/mnt/test/420-sock: No such file or directory
 Test a hard link to a file
+/mnt/test/420-sock: No such file or directory