Adding files for Ada

[Richard Kenner]

There is now a set of files for Ada that seem reasonable to add to the GCC
tree.  They would be in a separate (ada) subdirectory and no changes to other
files are needed for them to work.  If a machine does not already have GNAT
installed, that subdirectory will not be configured in (because it's mostly
in Ada).

Both to pick a good date and because I'll be away from tomorrow until May 30,
I propose adding the files on June 1.

Are there any objections/issues to doing so?