[dev.cc] runtime: fix bus error accessing auxv random data on arm5

It's rather unsporting of the kernel to give us a pointer to unaligned memory.

This fixes one crash, the next crash occurs in the soft float emulation.

LGTM=minux, rsc, austin
R=minux, rsc, austin
CC=golang-codereviews
https://codereview.appspot.com/177730043