runtime: work around 5c bug in GC code.
runtime: work around 5c bug in GC code.

5c miscompiles *p++ = struct_literal.

R=dave, golang-dev
CC=golang-dev
https://codereview.appspot.com/7065069
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go