dummy variable extraction on a function scope

Summary:
- Added extraction to a dummy variable
- using auto for the dummy variable type for now
- Works on a function scope
- Adding braces to create a compound statement not supported yet
- added unit tests

Reviewers: sammccall, kadircet

Subscribers: mgorny, jkorous, arphaman, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D63773

llvm-svn: 365453