[Bug ada/81878] --disable-bootstrap --enable-languages=ada fails

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81878

--- Comment #25 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
>> This change broke the mingw-w64 GCC 8 bootstrap on Windows. The cleanup
>> seems a bit too aggressive as now `-B ../..` is never passed down to xg++.
>
> That shouldn't happen though, see comment #16.

The error one of the users reported is
https://user-images.githubusercontent.com/216319/40851484-dbb095da-65c7-11e8-9b98-94ca80ab2b23.png

Which does indeed show that during the bootstrap -B to the right directory is
passed, and that the file is there.  So not sure why it's saying it can't find
it.  If that's the case that the paths are all correct, I'll go look into why
it's giving a file not found while the file is there.