[LyX/master] Avoid warnings about deprecated copy in gcc 10 too

[Richard Kimberly Heck]

On 4/30/20 6:28 AM, Jean-Marc Lasgouttes wrote:
> Le 30/04/2020 à 11:48, Jean-Marc Lasgouttes a écrit :
>> commit db5021c42eb5828c3fa0fd786b14eafcf9fed52f
>> Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
>> Date:   Thu Apr 30 12:09:17 2020 +0200
>>
>>      Avoid warnings about deprecated copy in gcc 10 too
>
> Riki, do you want all the warning-related fixes in branch too?

I haven't been doing that myself. But it's not harm.

Riki