Unqualified jobs, which rely on the default compiler, are gone.
Qualified jobs explicitly configure either clang or gcc and use the
appropriate suffix. Qualified jobs have needs/depends set to empty to
both avoid waiting for previous stages to start and to avoid pulling in
artifacts from the previous stage.

Qualified jobs inhabit two new lanes: build-gcc and build-clang, to
visually break the already long column of "build" jobs.

Job ordering within a lane is not exactly matching, gcc-clang. This is
noticeable with the jobs using the "extra" suffix. The reason for this
is unclear.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>