[RFA]: Turn on Ada support

[Paul Hilfinger]

> The changes to symtab.c, symfile.c, defs.h, and gdbtypes.h are fine.
> 
> I don't like the braces around the lone 'return' statements in
> symtab.c, though.  I don't think they add much, although what's
> probably more germane is that it's not the typical practice elsewhere
> in the code.

Jim,

Great!  I'll remove the braces; they're probably an artifact of some
internal change sequence anyway.

Paul