cdk_compat(3) on Linux

The text d8e40952ed6e, as Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy) shipped it.

Cdk4 compatibility functions

cdk_compat(3) on Linux now