mdist: Ensure correct format for sha256sum.
mdist: Ensure correct format for sha256sum.

We conform to the format described at
<https://www.gnu.org/software/coreutils/manual/html_node/md5sum-invocation.html>.
and compatible with busybox and Perl's shasum utility.

pexip/meson,pexip/meson,jpakkane/meson,pexip/meson,QuLogic/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,jpakkane/meson,QuLogic/meson,mesonbuild/meson,mesonbuild/meson,QuLogic/meson,mesonbuild/meson,QuLogic/meson,jpakkane/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,jpakkane/meson,jpakkane/meson,jpakkane/meson,jpakkane/meson,QuLogic/meson,jpakkane/meson,mesonbuild/meson,QuLogic/meson,QuLogic/meson,jpakkane/meson,QuLogic/meson,QuLogic/meson,pexip/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson