O_CLOEXEC is needed.
* nis/nss_compat/compat-grp.c: Use 'e' flag when opening file.
Avoid additional fcntl to set O_CLOEXEC if not needed.
* nis/nss_compat/compat-initgroups.c: Likewise.
* nis/nss_compat/compat-pwd.c: Likewise.
* nis/nss_compat/compat-spwd.c: Likewise.