This is needed when we are re-building to the wasm target.

Fixes #25774

Change-Id: I5dc47bd7e56c8570b8d2485273ef0d10f2feac6f
Reviewed-on: https://go-review.googlesource.com/116915Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>