Added because CTest has no convenient way to set environment vars for commands it runs.
--env-system-config -> BLENDER_SYSTEM_CONFIG
--env-system-datafiles -> BLENDER_SYSTEM_DATAFILES
--env-system-scripts -> BLENDER_SYSTEM_SCRIPTS
--env-system-plugins -> BLENDER_SYSTEM_PLUGINS
--env-system-python -> BLENDER_SYSTEM_PYTHON