Summary:
From <pwd.h>: user_from_uid, uid_from_user

From <grp.h>: group_from_gid, gid_from_group

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, vitalybuka

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D42068

llvm-svn: 322829