libpam: Fix build with eglibc 2.16

libpam: Fix build with eglibc 2.16

pam_unix_acct.c: In function '_unix_run_verify_binary':
pam_unix_acct.c:97:19: error: storage size of 'rlim' isn't known
pam_unix_acct.c:106:19: error: 'RLIMIT_NOFILE' undeclared (first use in
this function)
pam_unix_acct.c:106:19: note: each undeclared identifier is reported
only once for each function it appears in

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>