linux-pam: fix missing includes

Two patches taken from upstream fix e.g.
http://autobuild.buildroot.org/results/fa31431066ce0f9c554bdb923e59aa0458508224



These patches are in linux-pam 1.1.6 already, but since I don't know
how to test it, I don't want to do a version bump.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>