Fix format script for Ubuntu (#9028)

Summary:
I get `clang-format-diff` after running `apt install clang-format` on Ubuntu instead of `clang-format-diff.py`. So I think it makes sense to make the format script compatible with this behavior.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9028

Reviewed By: ajkr

Differential Revision: D31634041

Pulled By: jay-zhuang

fbshipit-source-id: b936de791ddcafa6ff304039ef33936e1e04864d

build_tools/format-diff.sh

@@ -38,7 +38,9 @@ if [ "$CLANG_FORMAT_DIFF" ]; then
   fi
 else
   # First try directly executing the possibilities
-  if clang-format-diff.py --help &> /dev/null < /dev/null; then
+  if clang-format-diff --help &> /dev/null < /dev/null; then
+    CLANG_FORMAT_DIFF=clang-format-diff
+  elif clang-format-diff.py --help &> /dev/null < /dev/null; then
     CLANG_FORMAT_DIFF=clang-format-diff.py
   elif $REPO_ROOT/clang-format-diff.py --help &> /dev/null < /dev/null; then
     CLANG_FORMAT_DIFF=$REPO_ROOT/clang-format-diff.py