[39/46] Change STMT_VINFO_UNALIGNED_DR to a dr_vec_info

[39/46] Change STMT_VINFO_UNALIGNED_DR to a dr_vec_info

After previous changes, it makes more sense for STMT_VINFO_UNALIGNED_DR
to be dr_vec_info rather than a data_reference.

2018-07-31  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vectorizer.h (_loop_vec_info::unaligned_dr): Change to
	dr_vec_info.
	* tree-vect-data-refs.c (vect_enhance_data_refs_alignment): Update
	accordingly.
	* tree-vect-loop.c (vect_analyze_loop_2): Likewise.
	* tree-vect-loop-manip.c (get_misalign_in_elems): Likewise.
	(vect_gen_prolog_loop_niters): Likewise.

From-SVN: r263154