[PATCH] Ensure mktime sets errno on error (bug 23789)

[Paul Eggert]

On 10/26/18 2:18 PM, Albert ARIBAUD wrote:
> Is it allowed behavior to
> alter errno when not returning an error condition?

Ordinarily yes. But it would be better if mktime left errno alone when 
-1 does not represent an error, so that the caller can easily 
distinguish valid -1 return values from erroneous ones.