FR: enable pam_debug in all builds, not just debug

We had several cases by now where the pam_debug output would have been useful to figure out auth_pam setup problems on the PAM side, but this functionality is only available in debug builds.

As the space and performance overhead of these few PAM debug messages are rather minimal, and only get evaluated once per connection attempt, I don't see a problem with having these compiled into regular releases so that we can make use of pam_debug without getting a debug build of the auth_pam.so / auth_pam_v1.so first.