This patch carries over fortran gang parsing updates I recently applied
to trunk to gomp-4_0-branch. Most of it was straightforward, but I did
take the opportunity to clean up struct gfc_omp_clauses by eliminating
some unnecessary bits for num_gangs, num_workers, vector_length and
tile. Besides that, this patch does diverge from trunk a little because
gomp4's preliminary support for device_type.

Tom, while I was working on combined loop splitter, I noticed that
reductions in combined constructs were still being associated with the
parallel/kernels constructs. I've updated it to match the behavior in
your c FE patch, i.e., reductions in combined constructs are only
associated with the split acc loop. Let me know if that's causes any
problems with you. This is how trunk behaves now.

Another random note. I'm not sure why gfortran ICEs when I associate the
private clauses in combined constructs with the acc loop. That code was
ifdef'ed out in gfc_filter_oacc_combined_clauses. I'll investigate this
later.

I've applied this patch to gomp-4_0-branch.

Cesar