Run clang tidy in parallel

tools/run-clang-tidy

 #!/usr/bin/env bash
+set -euo pipefail
 
 SCRIPTDIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"
 ROOTDIR="$(realpath "${SCRIPTDIR}/..")"
@@ -23,9 +24,7 @@ RUN_CLANG_TIDY_CANDIDATES=(
 	/usr/share/clang/run-clang-tidy.py
 )
 
-RUN_CLANG_TIDY=""
-
-for candidate in ${RUN_CLANG_TIDY_CANDIDATES[@]}; do
+for candidate in "${RUN_CLANG_TIDY_CANDIDATES[@]}"; do
 	if ! command -v "${candidate}"; then
 		continue;
 	fi
@@ -34,9 +33,13 @@ for candidate in ${RUN_CLANG_TIDY_CANDIDATES[@]}; do
 	break;
 done
 
-if [[ -z "${RUN_CLANG_TIDY}" ]]; then
+if [[ ! -v RUN_CLANG_TIDY ]]; then
 	echo "No run-clang-tidy executable found"
 	exit 1
 fi
 
-${RUN_CLANG_TIDY} -p "${ROOTDIR}/compile_commands_wo_subprojects/"
+JOBS=$(nproc)
+
+${RUN_CLANG_TIDY} \
+	-p "${ROOTDIR}/compile_commands_wo_subprojects/" \
+	-j "${JOBS}"