select: use correct SIZEOF_ constant

At least under Windows, there is no SIZEOF_LONG, so it evaluates to 0 even
though sizeof(int) == sizeof(long). This should probably have been
CURL_SIZEOF_LONG, but the type of timeout_ms changed from long to time_t
anyway.
This triggered MSVC warning C4668 about implicitly replacing undefined
macros with '0'.

Closes #1362

lib/select.c

@@ -164,7 +164,7 @@ int Curl_socket_check(curl_socket_t readfd0, /* two sockets to read from */
   int r;
   int ret;
 
-#if SIZEOF_LONG != SIZEOF_INT
+#if SIZEOF_TIME_T != SIZEOF_INT
   /* wrap-around precaution */
   if(timeout_ms >= INT_MAX)
     timeout_ms = INT_MAX;