When meson runs a dist script it sets both MESON_BUILD_ROOT and
MESON_DIST_ROOT envvars [1]. But for some reason, we took the
former as an argument and obtained the latter via env. Well,
obtain both via env.
1: https://mesonbuild.com/Reference-manual_builtin_meson.html#mesonadd_dist_script
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>