Avoid column limit violation in block comments in certain cases.

Summary:
Add penalty when an excessively long line in a block comment can not be
broken on a leading whitespace. Lack of this addition can lead to severe column
width violations when they can be easily avoided.

Reviewers: djasper

Reviewed By: djasper

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D1071

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@185337 91177308-0d34-0410-b5e6-96231b3b80d8