Run clang-format with make check

scripts/clang-format-check

@@ -5,6 +5,12 @@ if [ -n "$1" ]; then
     clangformat="clang-format-$1"
 fi
 
+if ! type $clangformat >/dev/null; then
+    # clang-format not found. If running tests, mark this test as
+    # skipped.
+    exit 77
+fi
+
 errors=0
 paths=$(find . -type f -a '(' -name '*.c' -o -name '*.h' ')')
 for path in $paths; do