[emacs] Indent statement continuation to match clang-format

Summary:
Was:

  int LongVariableName =
    veryLongFunctionNameThatExceeds80ColumnsRule(SomeParameter);

  int ShortVar = veryLongFunctionNameThatStillFitsIntoOneLine(SomeParameter)
    .nowThisDoesntFit()
    .andThis()

Now:

  int LongVariableName =
      veryLongFunctionNameThatExceeds80ColumnsRule(SomeParameter);

  int ShortVar = veryLongFunctionNameThatStillFitsIntoOneLine(SomeParameter)
                     .nowThisDoesntFit()
                     .andThis()


Reviewers: espindola, MaskRay

Reviewed By: MaskRay

Subscribers: greened, llvm-commits

Differential Revision: https://reviews.llvm.org/D49726

llvm-svn: 338686