Caldera had a Skunkware page for developers, last updated in 2001, which SCO never pulled down, so you can still view it. It had special instructions for OpenServer folks, such as, presumably, AutoZone back when it still was an OpenServer customer, telling them that even if they didn't have a licensed Caldera system, they were licensed to use "system libraries and headers" required by the gcc package for OpenServer. I would understand that to mean that they could use them for any version of Linux they wanted.