Add a script to check for clang-formattedness.

scripts/check-formatting.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+# The files that need to be properly formatted.  We'll grow this incrementally
+# until it includes all the jemalloc source files (as we convert things over),
+# and then just replace it with
+#    find -name '*.c' -o -name '*.h' -o -name '*.cpp
+FILES=(
+)
+
+if command -v clang-format &> /dev/null; then
+  CLANG_FORMAT="clang-format"
+elif command -v clang-format-8 &> /dev/null; then
+  CLANG_FORMAT="clang-format-8"
+else
+  echo "Couldn't find clang-format."
+fi
+
+if ! $CLANG_FORMAT -version | grep "version 8\." &> /dev/null; then
+  echo "clang-format is the wrong version."
+  exit 1
+fi
+
+for file in ${FILES[@]}; do
+  if ! cmp --silent $file <($CLANG_FORMAT $file) &> /dev/null; then
+    echo "Error: $file is not clang-formatted"
+    exit 1
+  fi
+done