[PATCH] Fix tst-setcontext9 for optimized small stacks.

[Florian Weimer]

* Carlos O'Donell:

> From 52d90e0548bee31f3f1cb62d63f40f31de5b1d97 Mon Sep 17 00:00:00 2001
> From: Carlos O'Donell <carlos@redhat.com>
> Date: Wed, 5 Sep 2018 01:16:42 -0400
> Subject: [PATCH] Fix tst-setcontext9 for optimized small stacks.

Even with this commit, the test still fails on POWER.  I filed:

  <https://sourceware.org/bugzilla/show_bug.cgi?id=23717>

Thanks,
Florian