torture: Handle systems lacking the mpstat command

The rcutorture scripting uses the mpstat command to determine how much
the system is being used, and adjusts make's -j argument accordingly.
However, mpstat isn't installed by default, so it would be good if the
scripting does something useful when mpstat isn't present.

This commit therefore makes the scripts assumes that if mpstat is not
present, they are free to use all the CPUs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/rcutorture/bin/cpus2use.sh

@@ -15,8 +15,15 @@ then
 	exit 0
 fi
 ncpus=`grep '^processor' /proc/cpuinfo | wc -l`
-idlecpus=`mpstat | tail -1 | \
-	awk -v ncpus=$ncpus '{ print ncpus * ($7 + $NF) / 100 }'`
+if mpstat -V > /dev/null 2>&1
+then
+	idlecpus=`mpstat | tail -1 | \
+		awk -v ncpus=$ncpus '{ print ncpus * ($7 + $NF) / 100 }'`
+else
+	# No mpstat command, so use all available CPUs.
+	echo The mpstat command is not available, so greedily using all CPUs.
+	idlecpus=$ncpus
+fi
 awk -v ncpus=$ncpus -v idlecpus=$idlecpus < /dev/null '
 BEGIN {
 	cpus2use = idlecpus;