Re: Thread-unsafe coding in ecpg

I wrote:
> On the third hand, the lack of previous reports suggests that maybe
> this whole thing is seldom a problem in practice. Maybe we should
> just use uselocale() where available and otherwise hope it's OK
> to keep on doing what we were doing.

If we go with that approach, I think we need to adapt the patch
as attached. I autoconfiscated it and fixed a portability problem
(it didn't compile on macOS, which has these decls in <xlocale.h>).

I've verified that this fixes the problem I was seeing on OpenBSD 6.4.
I've not bothered to test on a platform lacking uselocale() --- I
think it's clear by inspection that the patch doesn't change anything
in that case.

Not sure if we need to document this or not. On platforms with
uselocale(), it should fix the problem without any need for user
attention. On platforms without, there's no change, and given
the lack of previous complaints I'm not sure it's really an issue.

regards, tom lane