Summary: Add missing flag to UsersManual
It would be good to merge it to 4.0 branch.

Reviewers: hans

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D28727

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@292112 91177308-0d34-0410-b5e6-96231b3b80d8