committed: merge with libada-branch

[Zack Weinberg]

So, what this gives us is a wrapper Makefile in libada/ that invokes
gcc/Makefile to do all the work.  None of the code is moved.  This is
a step forward, but the multilibs logic is very fragile, and I doubt
it can be made to work without physically moving all of the libada
source code into the libada directory (I could be wrong about this).

What are your future plans for this directory?

zw