introudce handle_t and arity_t

Android: /assets and debugging

C/threads.c

@@ -700,11 +700,15 @@ p_thread_set_concurrency( USES_REGS1 )
     Yap_Error(TYPE_ERROR_INTEGER,tnew,"thread_set_concurrency/2");
     return(FALSE);
   }
+#if HAVE_PTHREAD_GETCONCURRENCY
   cur = MkIntegerTerm(pthread_getconcurrency());
   if (pthread_setconcurrency(newc) != 0) {
     return FALSE;
   }
   return Yap_unify(ARG1, MkIntegerTerm(cur));
+#else
+  return FALSE;
+#endif
 }
 
 static Int