runtime: fix arm softfloat again for R12
runtime: fix arm softfloat again for R12

Missed a case, so now generalized.

R=ken2
CC=golang-dev
http://codereview.appspot.com/2540042
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go