Do not build .mo files in source directory (bug 14121)

[Florian Weimer]

On 12/14/2017 10:46 PM, Joseph Myers wrote:
> 2017-12-14  Joseph Myers<joseph@codesourcery.com>
> 
> 	[BZ #14121]
> 	* po/Makefile (generated): Add $(ALL_LINGUAS:%=%.mo).
> 	(%.mo): Change to $(objpfx)%.mo.  Use $(make-target-directory).
> 	($(mo-installed)): Use $(objpfx)%.mo.
> 	(realclean): Remove rule.

Looks okay to me.

Thanks,
Florian