Makefiles don't do comments, so these were forwarded into the variable.
*Most* users would expand the arguments to a shell where it'd be
ignored, but not all of them.
Contributes-To: https://github.com/RIOT-OS/RIOT/pull/18489
(This is also where the one version that is added here was removed).
Redirecting `2>&1 >/dev/null` moves stderr to stdout first and then
stdout to /dev/null; when checking for command existence or otherwise
silencing output, this is usually not desired (but only starts producing
errors when the actual command fails, which is often not tested).
