Retain isImplicit flag for local variable declarations when instantiating
templates.

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D3924

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@209686 91177308-0d34-0410-b5e6-96231b3b80d8