[gomp4] Some progress on #pragma omp simd

[Aldy Hernandez]

> I am not sure about the upcoming spec, but as per today's spec
> vectorlength in pragma simd can have multiple parameters and so I
> think it would be a good idea to use a max.

As discussed here:

http://software.intel.com/en-us/forums/topic/391056

"The use of multiple vectorlength arguments is being removed (or at 
least deprecated) in the next revision of the spec., since it carries no 
semantic meaning and is not even a very good hint to the compiler."

If/when we merge into mainline, I am pretty sure the latest spec will be 
out, so there's little sense in spending time on implementing things 
that will be obsolete by the time we release.  Disallowing multiple 
vectorlengths makes it trivial to just use OpenMP's safelen clause 
without any additional code.

Aldy