[sanitizer] Correct alignment of x32 __sanitizer_siginfo

Since alignment of x32 siginfo_t is 8 bytes, not 4 bytes, use u64 in
__sanitizer_siginfo_pad to align x32 __sanitizer_siginfo to 8 bytes.

Fixes llvm#62394

Differential Revision: https://reviews.llvm.org/D149309

Author: hjl-tools

compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h

@@ -578,8 +578,13 @@ struct __sanitizer_sigset_t {
 #endif
 
 struct __sanitizer_siginfo_pad {
+#if SANITIZER_X32
+  // x32 siginfo_t is aligned to 8 bytes.
+  u64 pad[128 / sizeof(u64)];
+#else
   // Require uptr, because siginfo_t is always pointer-size aligned on Linux.
   uptr pad[128 / sizeof(uptr)];
+#endif
 };
 
 #if SANITIZER_LINUX