glx: turn LIBGL_NO_DRAWARRAYS into a boolean

Instead of setting based on set/unset, allow users to use boolean values.
In the docs, use `NO_DRAWARRAYS=true` instead of `NO_DRAWARRAYS=1` as it's
clearer IMO.

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
2 files changed