Ubuntu upgrade bug related to llvm packaging

[Brian Murray]

In Ubuntu there has been a bug[1] reported about users being unable to
upgrade from Ubuntu 18.04 LTS to Ubuntu 20.04 LTS. I've done a bit of
digging into it and discovered that it has to do with the "Breaks"
section of libomp5-9 and libomp5-10. Changing the "Breaks" version to
"(<< 3.7-1)" allows the upgrade between releases to proceed.
Additionally, just removing "Break" field from both of those packages
also works. The commit changing the Breaks to "libomp5 (<< 44)" can
first be found here:

https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/commit/d9b6d3fd40bc1079d47db90021e01d8bcd9a97b8

Discussing this matter with Julian Klode he suggested changing the
relationship between clang-9 and libomp-9-dev from a "Recommends" to a
"Suggests". This solution also works.

Naturally, I'm keen to sort this out so users can upgrade to the latest
LTS release of Ubuntu. I'm happy to do the work of uploading the change
for Ubuntu but I'm wondering what solution is best. Do you have any
input?

[1] http://launchpad.net/bugs/1886748

Thanks!
--
Brian Murray