clang-format: Support ObjC's NS_ENUMs.

Before:
  typedef NS_ENUM(NSInteger, MyType) {
      /// Information about someDecentlyLongValue.
      someDecentlyLongValue,
      /// Information about anotherDecentlyLongValue.
      anotherDecentlyLongValue,
      /// Information about aThirdDecentlyLongValue.
      aThirdDecentlyLongValue};

After:
  typedef NS_ENUM(NSInteger, MyType) {
    /// Information about someDecentlyLongValue.
    someDecentlyLongValue,
    /// Information about anotherDecentlyLongValue.
    anotherDecentlyLongValue,
    /// Information about aThirdDecentlyLongValue.
    aThirdDecentlyLongValue
  };

llvm-svn: 200469