PAM passwdqc, strict aliasing, and WARNS

Someone who has yet to confess added -Werror to the global CFLAGS
(via /etc/make.conf) for one of our systems at work.  Before I
figured out that this was the cause of builds failing, I hacked up
pam_passwdc to resolve the problem.  This gets the module to
WARNS=2, but to go farther, the "logically const" issues with this
code will need to be sorted out.

Is this change worth committing?  Is this the best way to resolve
the strict aliasing issues in this code?

Thanks,
Justin