Run clang-format on every commit

Test: repo upload --cbr .
Change-Id: Ib4bea4649320db8890399dda8a285bab69f4b482
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
new file mode 100644
index 0000000..7fb1636
--- /dev/null
+++ b/PREUPLOAD.cfg
@@ -0,0 +1,6 @@
+[Options]
+ignore_merged_commits = true
+
+[Builtin Hooks]
+clang_format = true
+