clang-format: Fix bad wrapping of ObjC method exprs.

Before:
  [aaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaa:
      aaaaaaaa aaa:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa];

After:
  [aaaaaaaaaaaaaaaaaaaaaaaaa
      aaaaaaaaaaaaaaaaa:aaaaaaaa
                    aaa:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa];

Note that this might now violate the column limit and we probably need an
alternative way of indenting these then. However, that is still strictly better
than the messy formatting that clang-format did before.

llvm-svn: 236598