message: check_format.sh: dump readable diff
  Also, check whether $CLANG_FORMAT executable exists at all
diff: @@ -40,6 +40,7 @@ version 12.0.0 is used for the check. Otherwise the result can ne unexpected.
  CLANG_FORMAT="clang-format"
  [[ ! -z $1 ]] && CLANG_FORMAT=$1
  +which "$CLANG_FORMAT" || { echo "No $CLANG_FORMAT found in PATH" && exit 1; }
  REQUIRED_VERSION="12.0.0"
  VERSION_STRING="clang-format version $REQUIRED_VERSION.*"
  CURRENT_VERSION="$($CLANG_FORMAT --version)"
  @@ -52,7 +53,7 @@ fi
  # For benchmarks folder do not check 03_complex, as these tests come from real projects with their formatting.
  FILES=`ls src/*.cpp src/*.h src/opt/*.cpp src/opt/*.h *.cpp builtins/builtins-c-* benchmarks/{01,02}*/*{cpp,ispc} common/*.h stdlib.ispc`
  for FILE in $FILES; do
  - $CLANG_FORMAT $FILE | cmp $FILE >/dev/null
  + diff -uN --label original/$FILE --label formatted/$FILE <(cat $FILE) <($CLANG_FORMAT $FILE)
  if [ $? -ne 0 ]; then
  echo "[!] INCORRECT FORMATTING! $FILE" >&2
  EXIT_CODE=1
  