[clang-format] Align trailing comments if ColumnLimit is 0

Summary:
ColumnLimit = 0 means no limit, so comment should always be aligned if requested. This was broken with

  https://llvm.org/svn/llvm-project/cfe/trunk@304687

introduced via

  https://reviews.llvm.org/D33830

and is included in 5.0.0-rc2. This commit fixes it and adds a unittest for this property.

Should go into clang-5.0 IMHO.

Contributed by @pboettch!

Reviewers: djasper, krasimir

Reviewed By: djasper, krasimir

Subscribers: hans, klimek

Differential Revision: https://reviews.llvm.org/D36967

llvm-svn: 311532