Avoid the following warning which fails a bot (via -Werror).
```
/tmp/gotsan.JfrpVPu7pG/gotsan.cc:10456:25: error: ‘_tsan_pointer_chk_guard’ initialized and declared ‘extern’ [-Werror]
extern "C" __tsan::uptr _tsan_pointer_chk_guard = 0;
^~~~~~~~~~~~~~~~~~~~~~~
```
llvm-svn: 364823
#if SANITIZER_LINUX && defined(__aarch64__)
void InitializeGuardPtr() __attribute__((visibility("hidden")));
-#endif
-// TODO(yln): only define this when necessary
extern "C" __tsan::uptr _tsan_pointer_chk_guard = 0;
+#endif
namespace __tsan {
return sp;
#endif
#elif defined(__aarch64__)
+# if SANITIZER_LINUX
return mangled_sp ^ _tsan_pointer_chk_guard;
+# else
+ return mangled_sp;
+# endif
#elif defined(__powerpc64__)
// Reverse of:
// ld r4, -28696(r13)