Do not insert backslashes, when breaking line comments after preprocessor directives.

Summary: This solves http://llvm.org/PR17536

Reviewers: klimek, djasper

Reviewed By: klimek

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D2142

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194491 91177308-0d34-0410-b5e6-96231b3b80d8