Add WLR_RENDERER_FORCE_SOFTWARE env var
We have WLR_RENDERER_ALLOW_SOFTWARE
to allow wlroots to run with a software renderer (which is not what a regular user would want). However, we don't have a way to make wlroots select a software rendering virtual device. This is useful to try out llvmpipe on a machine which does have a GPU.
Edited by Simon Ser