runtime/cgo: fix arm build
runtime/cgo: fix arm build

During my global search and replace I forgot to open *.S (capital).

R=golang-dev
TBR=golang-dev
CC=golang-dev
https://codereview.appspot.com/7415047

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang