This patch adjusts omp-low.c:expand_omp_for_generic() to expand to a "sequential"
loop form (without the OMP runtime calls), used for loop directives inside
OpenACC kernels constructs. Tom mentions that this allows the kernels parallelization
to work when '#pragma acc loop' makes the front-ends create OMP_FOR, which the
loop analysis phases don't understand.

Tested and committed to gomp-4_0-branch.

Chung-Lin

2015-06-16  Chung-Lin Tang  <cltang@codesourcery.com>

        * omp-low.c (struct omp_region): Add inside_kernels_p field.
        (expand_omp_for_generic): Adjust to generate a 'sequential' loop
        when GOMP builtin arguments are BUILT_IN_NONE.
        (expand_omp_for): Use expand_omp_for_generic() to generate a
        non-parallelized loop for OMP_FORs inside OpenACC kernels regions.
        (expand_omp): Mark inside_kernels_p field true for regions
        nested inside OpenACC kernels constructs.