[gtkada] parallel build support

[John Marino]

Since we are so chatty on gtkada mail list today...

I defined gtkada to build in parallel and it failed miserably.  I had to 
explicitly specify that gtkada must be built by 1 job serially.

If others can confirm that gtkada does not support parallel-building, 
might I request this feature?

I'd provide a patch but I don't know how to tell GNU make to do that 
properly.

Regards,
John