[3.14] gh-127081: use `getlogin_r` if available (gh-132751) (gh-135097)

The `getlogin` function is not thread-safe: replace with `getlogin_r` where
available.
(cherry picked from commit 1ffe913c2017b44804aca18befd45689df06c069)

Co-authored-by: Duane Griffin <duaneg@dghda.com>