fdc: always compile-check debug prints

Coverity noticed that some variables are only used by debug prints, and
called them unused. Always compile the print statements. While we're
here, print to stderr as well.

Bonus: Fix a debug printf I broke in f31937aa8

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[Touched up commit message. --js]
Message-id: 1454971529-14830-1-git-send-email-jsnow@redhat.com
