cherry pick openpam update

[emaste]

Summary

commit 893e4865617e4c1a8b8db734a1418bde61d19592 (HEAD -> stable/12)
Author: Dag-Erling Smørgrav <[e-mail]>
Date:   Mon Feb 25 18:41:16 2019 +0000

    Upgrade to OpenPAM Tabebuia.
    
    (cherry picked from commit 23d17223345108c52b96dcc5d7e6dab29e95f3e9)

via git cherry-pick -m 1 -x 23d17223345108c52b96dcc5d7e6dab29e95f3e9
PR 235903

[cem]

No objection in principle, but the diff is basically unreviewable as-is for me; it's like 90% autoconf generated shell.

[emaste]

In D28528#638545, @cem wrote:

No objection in principle, but the diff is basically unreviewable as-is for me; it's like 90% autoconf generated shell.

Indeed; I believe the only substantive change is in pam_getenv.c (and the addition of the test files).

It would be nice if autoconf used the @generated convention.