Use a non-recursive implementation to reconstruct line breaks.

Now that the TokenAnnotator does not require stack space anymore,
reconstructing the lines has become the limiting factor. This patch
fixes that problem, allowing large files with multiple megabytes of
single unwrapped lines to be formatted.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182861 91177308-0d34-0410-b5e6-96231b3b80d8