The most visible regressions are in ip6base and ip4 ACL tests.

The cause was tracked to be a downgrade (from clang-11 to clang-10) [0] of the compiler version used to build the VPP package.
As clang-11 is not the default installed version for Ubuntu 20.04, the VPP change is a usability fix (and the previous upgrade to clang-11 was the bug), so nothing to fix on either side.

[0] https://gerrit.fd.io/r/c/vpp/+/35967/6#message-dea58d4ded4eb7268a7a7124a37481f037d17150