[OPENMP 4.5] Sema/parsing support for extended format of 'schedule' clause.

OpenMP 4.0-3.1 supports the next format of ‘schedule’ clause: schedule(kind[, chunk_size])
Where kind can be one of ‘static’, ‘dynamic’, ‘guided’, ‘auto’ or ‘runtime’.
OpenMP 4.5 defines the format: schedule([modifier [, modifier]:]kind[, chunk_size])
Modifier can be one of ‘monotonic’, ‘nonmonotonic’ or ‘simd’.

llvm-svn: 256487