Backport some gcc9 fixes to branch

[Jean-Marc Lasgouttes]

Le 26/10/2019 à 05:01, Richard Kimberly Heck a écrit :
> On 10/25/19 1:13 PM, Jean-Marc Lasgouttes wrote:
>> Riki, is this OK?
>>
>> If this goes in, Kornel will probably have to backport some of his own
>> patches.
> 
> I know nothing about such things. If you think it's a good idea, please
> go ahead.

I pushed that to stable. Having less useless warnings allows to handle 
useful ones. Note that we are asking for trouble, since compilation is 
done with -Wall -Wextra :)

JMarc