[compiler-rt] fix __sanitizer_siginfo type on freebsd. (#77379)

mostly interested in the first half of the type, adding also compile
time check.

compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_freebsd.cpp

@@ -475,6 +475,8 @@ CHECK_TYPE_SIZE(nfds_t);
 CHECK_TYPE_SIZE(sigset_t);
 
 COMPILER_CHECK(sizeof(__sanitizer_sigaction) == sizeof(struct sigaction));
+COMPILER_CHECK(sizeof(__sanitizer_siginfo) == sizeof(siginfo_t));
+CHECK_SIZE_AND_OFFSET(siginfo_t, si_value);
 // Can't write checks for sa_handler and sa_sigaction due to them being
 // preprocessor macros.
 CHECK_STRUCT_SIZE_AND_OFFSET(sigaction, sa_mask);

compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_freebsd.h

@@ -301,11 +301,29 @@ struct __sanitizer_sigset_t {
 
 typedef __sanitizer_sigset_t __sanitizer_kernel_sigset_t;
 
+union __sanitizer_sigval {
+  int sival_int;
+  void *sival_ptr;
+};
+
 struct __sanitizer_siginfo {
-  // The size is determined by looking at sizeof of real siginfo_t on linux.
-  u64 opaque[128 / sizeof(u64)];
+  int si_signo;
+  int si_errno;
+  int si_code;
+  pid_t si_pid;
+  u32 si_uid;
+  int si_status;
+  void *si_addr;
+  union __sanitizer_sigval si_value;
+#  if SANITIZER_WORDSIZE == 64
+  char data[40];
+#  else
+  char data[32];
+#  endif
 };
 
+typedef __sanitizer_siginfo __sanitizer_siginfo_t;
+
 using __sanitizer_sighandler_ptr = void (*)(int sig);
 using __sanitizer_sigactionhandler_ptr = void (*)(int sig,
                                                   __sanitizer_siginfo *siginfo,