openmp: Use more efficient logical -> actual computation even if # iterations is...

openmp: Use more efficient logical -> actual computation even if # iterations is computed at runtime

For triangular loops use more efficient logical iteration number
to actual iterator values computation even for non-rectangular loops
where number of loop iterations could not be computed at compile time.

2020-08-05  Jakub Jelinek  <jakub@redhat.com>

	* omp-expand.c (expand_omp_for_init_counts): Remember
	first_inner_iterations, factor and n1o from the number of iterations
	computation in *fd.
	(expand_omp_for_init_vars): Use more efficient logical iteration number
	to actual iterator values computation even for non-rectangular loops
	where number of loop iterations could not be computed at compile time.

(cherry picked from commit 325714b4968050c927fe72f4a4ba860da2bf4ee2)