[Ada] Extensions of constrained discriminated with other progenitors

[Arnaud Charlet]

> For some reason this batch of changes caused parallel bootstrap
> on x86_64 to fail for me with linker errors linking the RTS complaining
> about x86_64_32 relocs and missing -fPIC.  A rm gcc/ada/rts/*.o and
> a build re-start gets me past this error.

I suspect this is a latent bug in the Makefile, unrelated to my changes.
FWIW, I always do a

rm -f x86_64-unknown-linux-gnu/libada/stamp-libada gcc/stamp-*

before starting a build, since since timestamp business simply does not
work in my experience and causes all kinds of troubles (such as the one
you've experienced I suspect).

Arno