coccinelle: implement parallel check

This patch is an implementation of parallel check of files. It uses
GNU parallel to run multiple spatch at once.
The concurrency level is set via the CONCURRENCY_LEVEL environment
variable.

qa/coccinelle/run_check.sh

@@ -19,11 +19,22 @@ else
 	PREFIX=$(git rev-parse --show-toplevel)/
 fi
 
+if [ -z "$CONCURRENCY_LEVEL" ]; then
+	CONCURRENCY_LEVEL=1
+	echo "No concurrency"
+else
+	echo "Using concurrency level $CONCURRENCY_LEVEL"
+fi
+
 for SMPL in $(git rev-parse --show-toplevel)/qa/coccinelle/*.cocci; do
 	echo "Testing cocci file: $SMPL"
-	for FILE in $LIST ; do
-		spatch --very-quiet -sp_file $SMPL --undefined UNITTESTS  $PREFIX$FILE || exit 1;
-	done
+	if command -v parallel >/dev/null; then
+		echo -n $LIST | parallel -d ' ' -j $CONCURRENCY_LEVEL spatch --very-quiet -sp_file $SMPL --undefined UNITTESTS $PREFIX{} || exit 1;
+	else
+		for FILE in $LIST ; do
+			spatch --very-quiet -sp_file $SMPL --undefined UNITTESTS  $PREFIX$FILE || exit 1;
+		done
+	fi
 done
 
 exit 0