[sanitizer] Fix sigaction definition on 32-bit sparc

[jrtc27]

Summary

D27301 was almost right, but not quite. This should fix it once and for all.

[jrtc27]

Full context included (not that it's really relevant...)

[jrtc27]

Reinstate compiler-rt/trunk/ prefix

[kcc]

LGTM

[jrtc27]

Ping; is there anything stopping this from being committed?

[m.ostapenko]

LGTM, thank you for fixing this! I'll apply this soon if nobody objects.

compiler-rt/trunk/lib/sanitizer_common/sanitizer_platform_limits_posix.h

 #ifndef __mips__
 #if defined(__sparc__)
 #if __GLIBC_PREREQ (2, 20)
-    // On sparc glibc 2.19 and earlier sa_flags was unsigned long, and
-    // __glibc_reserved0 didn't exist.
+    // On sparc glibc 2.19 and earlier sa_flags was unsigned long.
+#if defined(__arch64__)
+    // To maintain ABI compatibility on sparc64 when switching to an int,
+    // __glibc_reserved0 was added.
     int __glibc_reserved0;
+#endif
     int sa_flags;
 #else
     unsigned long sa_flags;