selftests/x86/protection_keys: Fix syscall NR redefinition warnings

On new enough glibc, the pkey syscalls numbers are available.  Check
first before defining them to avoid warnings like:

protection_keys.c:198:0: warning: "SYS_pkey_alloc" redefined
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1fbef53a9e6befb7165ff855fc1a7d4788a191d6.1509794321.git.luto@kernel.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

tools/testing/selftests/x86/protection_keys.c

@@ -189,17 +189,29 @@ void lots_o_noops_around_write(int *write_to_me)
 #define u64 uint64_t
 
 #ifdef __i386__
-#define SYS_mprotect_key 380
-#define SYS_pkey_alloc	 381
-#define SYS_pkey_free	 382
+
+#ifndef SYS_mprotect_key
+# define SYS_mprotect_key 380
+#endif
+#ifndef SYS_pkey_alloc
+# define SYS_pkey_alloc	 381
+# define SYS_pkey_free	 382
+#endif
 #define REG_IP_IDX REG_EIP
 #define si_pkey_offset 0x14
+
 #else
-#define SYS_mprotect_key 329
-#define SYS_pkey_alloc	 330
-#define SYS_pkey_free	 331
+
+#ifndef SYS_mprotect_key
+# define SYS_mprotect_key 329
+#endif
+#ifndef SYS_pkey_alloc
+# define SYS_pkey_alloc	 330
+# define SYS_pkey_free	 331
+#endif
 #define REG_IP_IDX REG_RIP
 #define si_pkey_offset 0x20
+
 #endif
 
 void dump_mem(void *dumpme, int len_bytes)