lib/: Set O_CLOEXEC for static FILE handles

lib/: Set O_CLOEXEC for static FILE handles

With glibc we can use "e" in mode argument to set O_CLOEXEC on
opened files. The /etc/shadow and /etc/gshadow file handles should
be protected to make sure that they are never passed to child
processes by accident.

Reviewed-by: Alejandro Colomar <alx@kernel.org>
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>