Cleanup libgomp's coalesce chunk data structures

	libgomp/
	* target.c (struct gomp_coalesce_chunk): New structure.
	(struct gomp_coalesce_buf): Update the chunks member to use that
	type.  Adjust all users.

Co-Authored-By: Cesar Philippidis <cesar@codesourcery.com>

From-SVN: r267446