title: Using Attribute Scalar_Storage_Order in ada with gcc 6.2.1
body: <p>I'm currently trying to find a solution to control the storage order for elements within a record in ADA.</p>
  <p>I'm using gcc 6.2.1 which doesnt recognize the <code>Scalar_Storage_Order</code> attribute ( even though the attribute is clearly referenced in the gcc 6.2 GNAT reference manual).</p>
  <pre><code>type Rec is record
  
        Data1 : T_Data;
        Data2 : T_Data;
  
     end record;
  
  for Rec use
        record
  
           Data1      at 0 range 0 .. 15;
           Data2      at 0 range 0 .. 15;
  
        end record;
  
  for Rec'Bit_Order use System.High_Order_First;
  for Rec'Scalar_Storage_Order use System.High_Order_First;
  
  error: unrecognized attribute &quot;Scalar_Storage_Order&quot;
  </code></pre>
  <p>Is there an alternative that I can use to achieve my goal?</p>