hppa: Fix setting of __libc_stack_end

The binutils package was recently changed to fix -z relro support on hppa.
See ld/21000 for details:
https://sourceware.org/bugzilla/show_bug.cgi?id=21000

This exposed a problem with the _dl_start_user function in the RTLD_START
define.  We need to set __libc_stack_end before it is made read only.  For
this, we need to define DL_STACK_END.  The offset of 0x160 gives the same
stack end as the code in _dl_start_user.

A build log with the attached patch is here:
https://buildd.debian.org/status/fetch.php?pkg=glibc&arch=hppa&ver=2.24-9&stamp=1487639205&raw=0