Move compute_alias_check_pairs to tree-data-ref.c

Move compute_alias_check_pairs to tree-data-ref.c

Move this function from tree-loop-distribution.c to tree-data-ref.c
and make it non-static to enable its use from other parts of GCC.

gcc/ChangeLog:
	* tree-loop-distribution.cc (data_ref_segment_size): Remove function.
	(latch_dominated_by_data_ref): Likewise.
	(compute_alias_check_pairs): Likewise.

	* tree-data-ref.cc (data_ref_segment_size): New function,
	copied from tree-loop-distribution.c
	(compute_alias_check_pairs): Likewise.
	(latch_dominated_by_data_ref): Likewise.

	* tree-data-ref.h (compute_alias_check_pairs): New declaration.