screen: bump to version 4.2.1

I re-did the patches: one patch per change, patch configure.in instead
of the configure script itself, a few more issues fixed. This should
hopefully make the patches acceptable for upstream, or at least make it
easier to migrate them on version bumps.

This also fixes compilation with musl libc.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>