C compilation fixes and hardening
Fix "implicit declaration of function ‘strlen’" in ipa_pwd_ntlm.c,
credits to Lukas.
Add -Werror=implicit-function-declaration to CFLAGS to point developers
to missing includes. It causes compilation to fail when a developer
forgets to add a required include. The problem is no longer hidden in a
massive wall of text from make.
Silence a harmless error from 389-DS slapi.h until the bug is fixed in
downstream, https://pagure.io/389-ds-base/issue/48979
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>