As libelf is a requirement for libbpf if it is not available, as in some
container build tests where NO_LIBELF=1 is used, then better warn about
the most basic library first.

Ditto for libz, check its availability before libbpf too.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/ZUEehyDk0FkPnvMR@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>