thread_pthread.c: use rb_pid_t

* thread_pthread.c (timer_thread_pipe.owner_process): process ID
  should be pid_t.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49796 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread_pthread.c

@@ -1266,7 +1266,7 @@ static int check_signal_thread_list(void) { return 0; }
 static struct {
     int normal[2];
     int low[2];
-    int owner_process;
+    rb_pid_t owner_process;
 } timer_thread_pipe = {
     {-1, -1},
     {-1, -1}, /* low priority */