ada/5911: Ada runtime and utilities should be broken out to their own directory

[Florian Weimer]

zack@codesourcery.com writes:

> The location of the Ada runtime and utilities is inconsistent
> with the location of all other language runtimes.  They
> should be moved to their own toplevel subdirectory, and their
> build harness brought into line with the other languages.

For technical reasons, the GNAT front end is built using the run-time
library sources which come with the compiler sources, and not using
the installed GNAT run-time library on the host system.  In other
words, the compiler depends on a (rather small) subset of the run-time
library sources.

However, there is no reason why a large part of the run-time library
could not be moved to a separate directory.  For the build, we should
use another separate directory, IMHO.