[Ada] Add obvious assertion

[Eric Botcazou]

This adds an obvious assertion in the N_Indexed_Component case of gnat_to_gnu 
so as to avoid the associated crash a few lines below.

Tested on x86_64-suse-linux, applied on the mainline.


2012-12-08  Eric Botcazou  <ebotca...@adacore.com>

        * gcc-interface/trans.c (gnat_to_gnu) <N_Indexed_Component>: Assert
        that the type of the prefix is ultimately an array.

-- 
Eric Botcazou
Index: gcc-interface/trans.c
===================================================================
--- gcc-interface/trans.c	(revision 194321)
+++ gcc-interface/trans.c	(working copy)
@@ -5410,6 +5410,10 @@ gnat_to_gnu (Node_Id gnat_node)
 
 	gnu_result = gnu_array_object;
 
+	/* The failure of this assertion will very likely come from a missing
+	   expansion for a packed array access.  */
+	gcc_assert (TREE_CODE (TREE_TYPE (gnu_array_object)) == ARRAY_TYPE);
+
 	/* First compute the number of dimensions of the array, then
 	   fill the expression array, the order depending on whether
 	   this is a Convention_Fortran array or not.  */