[OPENMP] Fix for LCV in simd directives in explicit clauses.

If loop control variable for simd-based directives is explicitly marked
as linear/lastprivate in clauses, codegen for such construct would
crash. Patch fixes this problem.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@267101 91177308-0d34-0410-b5e6-96231b3b80d8