[OPENMP 4.1] Add 'simd' clause for 'ordered' directive.

Parsing and sema analysis for 'simd' clause in 'ordered' directive.
Description
If the simd clause is specified, the ordered regions encountered by any thread will use only a single SIMD lane to execute the ordered
regions in the order of the loop iterations.
Restrictions
An ordered construct with the simd clause is the only OpenMP construct that can appear in the simd region

llvm-svn: 248696