deb-pkg: Make deb-pkg generate a seperate linux-libc-dev deb

userland dev likes latest incarnation of that userland API.
make it easy to also build it on make deb-pkg invocation:

dpkg-deb: building package `linux-libc-dev' in `../linux-libc-dev_2.6.32-rc6-4_amd64.deb'.

Last year patch rebased on top of latest deb-pkg changes.

Signed-off-by: maximilian attems <max@stro.at>
Signed-off-by: Michal Marek <mmarek@suse.cz>