cmd/dist: do not run race detector tests on netbsd

The race detector is not fully functional on NetBSD yet. Without
this change, all.bash fails in TestOutput.

This unbreaks the netbsd-amd64 builder.

Update #26403
Fixes #27268

Change-Id: I2c7015692d3632aa1037f40155d4fc5c7bb1d8c3
Reviewed-on: https://go-review.googlesource.com/131555Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/dist/test.go

@@ -1343,6 +1343,11 @@ func (t *tester) raceDetectorSupported() bool {
 	if isAlpineLinux() {
 		return false
 	}
+	// NetBSD support is unfinished.
+	// golang.org/issue/26403
+	if goos == "netbsd" {
+		return false
+	}
 	return true
 }