Added tests for testing migration of files in a compilation database.

This patch also fixes the case where a compilation database is autodetected from
source but the file itself cannot be found in the compilation database, it then
ignores the compilation database and transforms the file with c++11 support.


git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@191213 91177308-0d34-0410-b5e6-96231b3b80d8