feature/featuretags, all: add build features, use existing ones in more places

Saves 270 KB.

Updates #12614

Change-Id: I4c3fe06d32c49edb3a4bb0758a8617d83f291cf5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/magicsock/cloudinfo.go

@@ -17,6 +17,7 @@ import (
 	"strings"
 	"time"
 
+	"tailscale.com/feature/buildfeatures"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/cloudenv"
 )
@@ -34,6 +35,9 @@ type cloudInfo struct {
 }
 
 func newCloudInfo(logf logger.Logf) *cloudInfo {
+	if !buildfeatures.HasCloud {
+		return nil
+	}
 	tr := &http.Transport{
 		DisableKeepAlives: true,
 		Dial: (&net.Dialer{
@@ -53,6 +57,9 @@ func newCloudInfo(logf logger.Logf) *cloudInfo {
 // if the tailscaled process is running in a known cloud and there are any such
 // IPs present.
 func (ci *cloudInfo) GetPublicIPs(ctx context.Context) ([]netip.Addr, error) {
+	if !buildfeatures.HasCloud {
+		return nil, nil
+	}
 	switch ci.cloud {
 	case cloudenv.AWS:
 		ret, err := ci.getAWS(ctx)

wgengine/magicsock/magicsock_default.go

@@ -1,7 +1,7 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build !linux
+//go:build !linux || ts_omit_listenrawdisco
 
 package magicsock
 

wgengine/magicsock/magicsock_linux.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build linux && !ts_omit_listenrawdisco
+
 package magicsock
 
 import (

wgengine/userspace.go

@@ -435,7 +435,7 @@ func NewUserspaceEngine(logf logger.Logf, conf Config) (_ Engine, reterr error)
 	}
 	e.tundev.PreFilterPacketOutboundToWireGuardEngineIntercept = e.handleLocalPackets
 
-	if envknob.BoolDefaultTrue("TS_DEBUG_CONNECT_FAILURES") {
+	if buildfeatures.HasDebug && envknob.BoolDefaultTrue("TS_DEBUG_CONNECT_FAILURES") {
 		if e.tundev.PreFilterPacketInboundFromWireGuard != nil {
 			return nil, errors.New("unexpected PreFilterIn already set")
 		}