Support for the Open Virtual Memory System, a.k.a. VAX/VMS, operating system hasn't been maintained within Mesa since 2008. The proprietary OpenVMS operating system targets VAX/Alpha/Itanium hardware. OpenVMS uses a CDE-derived DECwindows MOTIF user-interface atop an X11-compliant windowing system. The last major release of OpenVMS was v8.4 in June of 2010.
Matt Turner writes on a patch to drop the support, "Not maintained since 2008. Doubtful that it's worked in quite a while."
Seeing this support set to be removed from Mesa isn't a huge loss since OpenVMS isn't a big target, there wasn't Gallium3D support, open-source graphics hardware drivers generally don't target this commercial OS, and the Mesa classic software rasterizer isn't too useful for end-users. Cutting out this OS code saves 2.388 lines of code.