[Ada] Set the mode of the record type crafted by make_aligning_type

[Olivier Hainque]

Olivier Hainque wrote:
> Committing to mainline.

> 	* decl.c (make_aligning_type): Set the mode of the RECORD_TYPE we
> 	craft and expand comment.

Forgot to mention: bootstrapped and tested on i686-pc-linux-gnu.