Update pddm to work with clang-format

Add clang-format off/on directives around pddm expansions to simplify formatting other code.
diff --git a/objectivec/GPBArray_PackagePrivate.h b/objectivec/GPBArray_PackagePrivate.h
index 35a4538..07eab89 100644
--- a/objectivec/GPBArray_PackagePrivate.h
+++ b/objectivec/GPBArray_PackagePrivate.h
@@ -54,6 +54,7 @@
 
 //%PDDM-EXPAND DECLARE_ARRAY_EXTRAS()
 // This block of code is generated, do not edit it directly.
+// clang-format off
 
 #pragma mark - Int32
 
@@ -119,6 +120,7 @@
 }
 @end
 
+// clang-format on
 //%PDDM-EXPAND-END DECLARE_ARRAY_EXTRAS()
 
 #pragma mark - NSArray Subclass