Split long strings on word boundaries.

Summary: Split strings at word boundaries, when there are no spaces and slashes.

Reviewers: klimek

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1003

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184304 91177308-0d34-0410-b5e6-96231b3b80d8