x86/mpx/selftests: Adjust the self-test to fresh distros that export the MPX ABI

Fix this warning:

  mpx-mini-test.c:422:0: warning: "SEGV_BNDERR" redefined

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: dave.hansen@intel.com
Cc: linux-mm@kvack.org
Cc: linuxram@us.ibm.com
Cc: mpe@ellerman.id.au
Cc: shakeelb@google.com
Cc: shuah@kernel.org
Link: http://lkml.kernel.org/r/20180514085908.GA12798@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tools/testing/selftests/x86/mpx-mini-test.c

@@ -368,6 +368,11 @@ static int expected_bnd_index = -1;
 uint64_t shadow_plb[NR_MPX_BOUNDS_REGISTERS][2]; /* shadow MPX bound registers */
 unsigned long shadow_map[NR_MPX_BOUNDS_REGISTERS];
 
+/* Failed address bound checks: */
+#ifndef SEGV_BNDERR
+# define SEGV_BNDERR	3
+#endif
+
 /*
  * The kernel is supposed to provide some information about the bounds
  * exception in the siginfo.  It should match what we have in the bounds
@@ -419,8 +424,6 @@ void handler(int signum, siginfo_t *si, void *vucontext)
 		br_count++;
 		dprintf1("#BR 0x%jx (total seen: %d)\n", status, br_count);
 
-#define SEGV_BNDERR     3  /* failed address bound checks */
-
 		dprintf2("Saw a #BR! status 0x%jx at %016lx br_reason: %jx\n",
 				status, ip, br_reason);
 		dprintf2("si_signo: %d\n", si->si_signo);