I downgraded xorg-x11 from the latest modular version to 6.8.2-r6. libXdmcp was
not installed for some reason, and other programs started complaining. I
unmerged and remerged xorg-x11, but it still wasn't installed.
Steps to Reproduce:
1. Downgrade from Modular xorg-x11
2. emerge xorg-x11
libXdmcp was not installed
This library should have been installed by the xorg-x11 ebuild.
6.8.2 does not build a shared version of libXdmcp, only static. You will need to
rebuild any packages that linked against a shared libXdmcp.