Adding systemd unit files for nscd

[Allan McRae]

I have noticed a number of Linux distributions starting to ship systemd
files for nscd.

To save each distribution having to generate/locate a copy of these
files, would it be acceptable to include them in glibc and take the
usual approach of having them installed when configuring the build with
--with-systemdsystemunitdir?

If so, I can review all the versions currently floating about and come
up with an appropriate version to include and do the necessary patching
of configure and Makefiles.

Allan