Remove "arch" usage in Documentation/features/list-arch.sh

Commit 669f6f96 introduced
the script list-arch.sh, which uses the command "arch":

ARCH=${1:-$(arch | sed 's/x86_64/x86/' | sed 's/i386/x86/')}

It turns out that the "arch" command does not exist in my system (arch
distro). Google found man pages which say "arch is deprecated command since
release util-linux 2.13. Use uname -m" (util-linux 2.13 was released in 2007).
I also found a debian bug reporting the lack of arch and being told to use
uname -m https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=446023

But then, why it works in some distros? Apparently coreutils gained an
optional arch command that needs to be explicitly enabled during compilation.
Some distros enable it, others don't. Sigh.
Signed-off-by: NDiego Calleja <diegocg@gmail.com>
Acked-by: NIngo Molnar <mingo@kernel.org>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/features/list-arch.sh

@@ -5,7 +5,7 @@
 # (If no arguments are given then it will print the host architecture's status.)
 #
 
-ARCH=${1:-$(arch | sed 's/x86_64/x86/' | sed 's/i386/x86/')}
+ARCH=${1:-$(uname -m | sed 's/x86_64/x86/' | sed 's/i386/x86/')}
 
 cd $(dirname $0)
 echo "#"