[PATCH] [OPENMP] First changes for Parsing and Sema for 'omp simd' directive support

[Richard Smith]

  LGTM

  Something to address in a future patch: it seems pointless for `OMPExecutableDirective` to have tail-allocated operands and to store `ArrayRef`s pointing to them. Either you should only store the number of each kind of operand and dynamically compute the locations of those arrays, or allocate them separately (the block allocator has no memory overhead, so this is exactly equivalent apart from marginally reducing space wasted to fragmentation).

http://llvm-reviews.chandlerc.com/D2815