cmd/racebuild: add netbsd/amd64

Updates golang/go#24354.
Updates golang/go#19273.
Updates golang/go#24322.

Change-Id: Ia67fde51d7698ca94d86c4697fd153a551a8ceee
Reviewed-on: https://go-review.googlesource.com/112880
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Author: Bryan C. Mills

cmd/racebuild/racebuild.go

@@ -79,6 +79,21 @@ cp compiler-rt/lib/tsan/go/race_linux_amd64.syso go/src/runtime/race
 (cd go/src && ./race.bash)
 			`,
 	},
+	&Platform{
+		OS:   "netbsd",
+		Arch: "amd64",
+		Type: "netbsd-amd64-8_0",
+		Script: `#!/usr/bin/env bash
+set -e
+git clone https://go.googlesource.com/go
+git clone http://llvm.org/git/compiler-rt.git
+(cd compiler-rt && git checkout $REV)
+(cd compiler-rt/lib/tsan/go && CC=clang ./buildgo.sh)
+cp compiler-rt/lib/tsan/go/race_netbsd_amd64.syso go/src/runtime/race
+# TODO(#24322): Uncomment to test the syso file before accepting it.
+# (cd go/src && ./race.bash)
+			`,
+	},
 	&Platform{
 		OS:   "windows",
 		Arch: "amd64",