shadow-native: Simplify and fix syslog disable patch

shadow-native: Simplify and fix syslog disable patch

Shadow is happily spamming the host syslog with messages and shouldn't be
which suggests the patch isn't working. Redo it to work at the configure
level which is simpler and hopefully more effective.

This is a squashed cherry-pick of commit 8f181686 (shadow-native:
Simplify and fix syslog disable patch) and commit e1f21d0d (shadow:
Disable the use of syslog() for the native tools).

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>