Merge branch 'bpf-selftest-clang-fixes'

Stanislav Fomichev says:

====================
This series contains small fixes to make bpf selftests compile cleanly
with clangs. All of them are not real problems, but it's nice to have
an option to use clang for the tests themselves.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>