Summary:
This patch adds a `SortUsingDeclaration` style option and enables it for llvm
style.

Reviewers: klimek

Reviewed By: klimek

Subscribers: klimek

Differential Revision: https://reviews.llvm.org/D34453

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@306094 91177308-0d34-0410-b5e6-96231b3b80d8