pam: stop building it wrong

pam: stop building it wrong

in the new lwp/pthread/shared universe, well, we have the
opportunity to be correct. and we chose to do it entirely wrong.
we're building a shared object. use the right rules. we need
to add some CFLAGS for PAM. do that using MODULE_CFLAGS instead
of just building a whole new CCRULE

Change-Id: Ie3e3c5ba902e5364cfa99d4dbd1b5b7fd4451127
Reviewed-on: http://gerrit.openafs.org/5153
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>