Move non-executable stack assembly code to end of file

Move non-executable stack assembly code to end of file

The non-executable stack annotation used for Linux works by adding
an additional section to the generated object.  The annotation added
in 9bfd03d723a9cf17673f40513a7adde1d503bcbc was added to the beginning
of each assembly file.  This caused build failures on Linux s390
because the remainder of the assembly code was then put in that
section, which was discarded during linking.

Add the annotation to the end of each assembly file instead, following
the instructions at:

    http://www.gentoo.org/proj/en/hardened/gnu-stack.xml

Change-Id: I5bd2d8d0ac31932b59757dcec0a942c459d61cac
Reviewed-on: http://gerrit.openafs.org/1615
Tested-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 9dbe48ac2d14742d2acefb9cb4138b810a1a128e)