[PATCH v2 1/3] posix: Add internal symbols for posix_spawn interface

[Florian Weimer]

* Albert ARIBAUD:

> The ChangeLog date on the master branch for this patch is off by one
> month (2018-09-24 instead of 2018-10-24).

Oops.  Please fix it in a new commit.  Thanks.

Florian