[OPENMP] Small refactoring of EmitOMPSimdLoop helper routine.

No functional changes intended.
Renamed EmitOMPSimdLoop to EmitOMPInnerLoop, I plan to re-use
it to emit inner loop in the future patches for CodeGen of the
worksharing loop directives (omp for, omp for simd).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219195 91177308-0d34-0410-b5e6-96231b3b80d8