tsan: use pthread_equal instead of direct pthread_t comparison

[dvyukov]

Summary

man pthread_equal:

The pthread_equal() function is necessary because thread IDs
should be considered opaque: there is no portable way for
applications to directly compare two pthread_t values.

Depends on D113916.

compiler-rt/lib/tsan/rtl/tsan_interceptors_posix.cpp

TSAN_INTERCEPTOR(int, kill, int pid, int sig) {
   return res;
 }
 
 TSAN_INTERCEPTOR(int, pthread_kill, void *tid, int sig) {
   SCOPED_TSAN_INTERCEPTOR(pthread_kill, tid, sig);
   ThreadSignalContext *sctx = SigCtx(thr);
   CHECK_NE(sctx, 0);
   int prev = sctx->int_signal_send;
-  if (tid == pthread_self()) {
+  bool self = pthread_equal(tid, pthread_self());
+  if (self)
     sctx->int_signal_send = sig;
-  }
   int res = REAL(pthread_kill)(tid, sig);
-  if (tid == pthread_self()) {
+  if (self) {
     CHECK_EQ(sctx->int_signal_send, sig);
     sctx->int_signal_send = prev;
   }
   return res;
 }
 
 TSAN_INTERCEPTOR(int, gettimeofday, void *tv, void *tz) {
   SCOPED_TSAN_INTERCEPTOR(gettimeofday, tv, tz);