(store_one_arg): Allow stack_slot to be SP in ARGS_GROW_DOWNWARD case.

From-SVN: r14639
diff --git a/gcc/calls.c b/gcc/calls.c
index 2ae1b31d..cdc999a 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -3436,7 +3436,7 @@
       if (GET_CODE (XEXP (arg->stack_slot, 0)) == PLUS)
 	upper_bound = -INTVAL (XEXP (XEXP (arg->stack_slot, 0), 1)) + 1;
       else
-	abort ();
+	upper_bound = 0;
 
       lower_bound = upper_bound - arg->size.constant;
 #else