Add a PREUPLOAD.cfg file to enable clang-format

This will save some time on reviews. This also preemptively formats some
stuff so that future developers don't have to fight against it.

Bug: None
Test: pre-upload.py complained when I introduced a badly formatted
      change.

Change-Id: I75b38cebc1298e481e62dbc9cea72f39ce33f88f
diff --git a/PREUPLOAD.cfg b/PREUPLOAD.cfg
new file mode 100644
index 0000000..254a062
--- /dev/null
+++ b/PREUPLOAD.cfg
@@ -0,0 +1,5 @@
+[Builtin Hooks]
+clang_format = true
+
+[Builtin Hooks Options]
+clang_format = --commit ${PREUPLOAD_COMMIT} --style file --extensions c