Fixes misc/cgo/testsigfwd, enabled for mips{,le} with the next commit
(https://golang.org/cl/34646).

Change-Id: I2bec894b0492fd4d84dd73a4faa19eafca760107
Reviewed-on: https://go-review.googlesource.com/34645Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>