regression in meson build, AC_PATH_PROG lost

autoconf allows to specify the path to a runtime binary that is not required during build via an environment variable: AC_PATH_PROG([PARTED], [parted], [], [$LIBVIRT_SBIN_PATH]) meson lacks such essential feature. As a result the package build environment needs to have more packages than necessary installed. This excessive list also pushes libvirt closer to the end of the build dependency chain. Was this considered while the buildsystem was switched to meson? Since meson does not support environment variables it seems the only way to address this is to introduce an option in meson_options.txt for each runtime executable. Will such change be accepted? Olaf