Support for CR LF newlines.

Summary:
reformat() tries to determine the newline style used in the input
(either LF or CR LF), and uses it for the output. Maybe not every single case is
supported, but at least the bug described in http://llvm.org/PR17182 should be
resolved.

Reviewers: djasper

Reviewed By: djasper

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D1643

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190519 91177308-0d34-0410-b5e6-96231b3b80d8