[OPENMP 4.1] Allow variables with reference types in private clauses.

OpenMP 4.1 allows to use variables with reference types in all private clauses (private, firstprivate, lastprivate, linear etc.). Patch allows to use such variables and fixes codegen for linear variables with reference types.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@245268 91177308-0d34-0410-b5e6-96231b3b80d8