cmd/5g: fix fixedtests/issue4396b.go test failure on arm5
cmd/5g: fix fixedtests/issue4396b.go test failure on arm5

Add missing file that should have been included in CL 6854063 / 5eac1a2d6fc3

R=remyoudompheng, minux.ma, rsc
CC=golang-dev
https://codereview.appspot.com/6891049

gnanderson/go,dsriram/golang,pombredanne/go-deleteme,apparentlymart/golang,tv42/old-go,tv42/old-go,apparentlymart/golang,apparentlymart/golang,dsriram/golang,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang,gnanderson/go,gnanderson/go,gnanderson/go,dsriram/golang,dsriram/golang,gnanderson/go,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,tv42/old-go