[OPENMP] 'omp teams' directive basic support.
Includes parsing and semantic analysis for 'omp teams' directive support from OpenMP 4.0. Adds additional analysis to 'omp target' directive with 'omp teams' directive.  


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219385 91177308-0d34-0410-b5e6-96231b3b80d8