When in pre-c++11 mode, treat _T("xxx") as a single string literal, repeat the _T() part around each fragment. This addresses http://llvm.org/PR17122

Reviewers: djasper

Reviewed By: djasper

CC: cfe-commits, klimek, rsmith

Differential Revision: http://llvm-reviews.chandlerc.com/D1640

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190804 91177308-0d34-0410-b5e6-96231b3b80d8