FreeBSD,OpenBSD: Improvements for environmental support are needed.

Currently, the FreeBSD maintainers of the CMake package need to apply several patches to CMake itself in order to build their package. This includes path replacements so that CMake respects $LOCALBASE over /usr/lib correctly and a few environmental fixes for packages.

The $LOCALBASE issue is also present on OpenBSD, and is being addressed in the platform file by setting a prefix path. This however does not support moving /usr/X11R6 to another folder yet^[1] and causes inconsistencies with hardcoded guesses in various CMake standard modules assuming that $LOCALBASE and /usr/local are the same.

^[1] The OPENBSD_X11BASE variable is not being used at all and isn't being respected either. On FreeBSD, this should be set to $PREFIX.