- explicitly check against NULL to avoid some compiler warnings - fix const cast-away. - Since we include <syslog.h> unconditionally allow syslog use on other   unixes, not just linux. We check that we provide a LOG_DEBUG macro instead.
- explicitly check against NULL to avoid some compiler warnings
- fix const cast-away.
- Since we include <syslog.h> unconditionally allow syslog use on other
  unixes, not just linux. We check that we provide a LOG_DEBUG macro instead.

Yubico/pam-u2f,Yubico/pam-u2f,Yubico/pam-u2f