compat: ckmake: make return code 2 is error

If make returns 2 it should be treat as an error and not as ok.
The documentation says 2 is returned if make encountered an error:
https://www.gnu.org/software/make/manual/html_node/Running.html

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
compat: backport nla_put_be{16,32,64}()

I intend to use these in nl80211.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
compat: ckmake: remove lots of warning spam for the log

Set the environment variable KCFLAGS = "-Wno-unused-but-set-variable"
to remove lots of spam from the log.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>