since focal is default; use default clang

[psi29a]

No description provided.

[akortunov]

Are you sure that there is no way to avoid 32-bit packages here? It seems that Travis can not find suitable 32-bit libc version.

[akortunov]

Also looks like "ubuntu9.3" update was removed due to regression, and 9.2 should be used instead. I wonder why Travis still tries to install buggy version... Probably maintainers of one of mirrors forgot to remove broken packages.

[psi29a]

looks like something broke, I'm assuming that they are using focal proposed and focal backports... that can lead to problems.

Yeah, clang problem is that it depends on depends that depend on depends... all the way down to a libc version that can't be installed as it was removed.

[akortunov]

I suppose that this PR can be closed.

[psi29a]

Maybe, I don't think it's simple any more to maintain these. Including MSVC2017, though I think that can be fixed if someone took the time to setup MSVC2017.