CI: Make build logs more readable

CI: Make build logs more readable

If make fails in a multi-process invocation, the log is pretty much
unreadable.  To make it readable, build as much as can be built without
failing.  Then run a single-process make again.  If we succeeded
previously, this should be a no-op.  If not, this run will stop at the
first error, which should be more readable, and will only print the few
lines we're interested in.

This has some side effects:  Now we build as much as we can, instead of
failing as early as possible; this may make CI a bit slower.  However,
it also has the benefit that you see _all_ the error messages that could
be given, instead of needing to fix the first error to see the next and
so on.

Cc: Iker Pedrosa <ipedrosa@redhat.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>