We couldn't do this before because sighandler was compiled for nacl.

Updates #30439

Change-Id: Ieec9938b6a1796c48d251cd8b1db1a42c25f3943
Reviewed-on: https://go-review.googlesource.com/c/go/+/200739
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>