When/how is global "errno" variable from reent.c to be used?

[Grant Edwards]

On 2020-10-16, Richard Damon <Richard@Damon-Family.org> wrote:

> Software the explicitly declares errno as
> extern int errno;
> is broken, and violates the C standard, and creates explicitly stated
> Undefined Behavior.

So the LWIP source is just plain wrong.

What is the global 'int errno' exported by reent.c for?

--
Grant