runtime: only use PPC GNU/Linux register code on little endian

Reportedly the current code builds on little endian but not big endian.

Fixes https://gcc.gnu.org/PR81893.

Change-Id: I90208c4ec5d2fb3bb00fde9da54f13660129b772
Reviewed-on: https://go-review.googlesource.com/57110
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Avelino <t@avelino.xxx>
1 file changed