auto-inc-dec: Set alignment properly

When auto-inc-dec creates a new mem to compute the cost of doing some
transform, it forgets to copy over the alignment of the original mem.
This gives wrong costs, for example, for rs6000 a floating point load
or store is hugely expensive if unaligned.  This patch fixes it.


	* auto-inc-dec.c (attempt_change): Set the alignment of the
	temporary memory to that of the original.

From-SVN: r270419