thread.c: int32_t instead of suseconds_t

* thread.c (timeval_for): cast to int32_t instead of suseconds_t,
  which is not defined non-POSIX platforms.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62276 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread.c

@@ -225,7 +225,7 @@ timeval_for(struct timeval *tv, const struct timespec *ts)
 {
     if (tv && ts) {
         tv->tv_sec = ts->tv_sec;
-        tv->tv_usec = (suseconds_t)(ts->tv_nsec / 1000);
+        tv->tv_usec = (int32_t)(ts->tv_nsec / 1000); /* 10**6 < 2**(32-1) */
         return tv;
     }
     return 0;