feat: implement darwin boottime without using cgo

Use sysctl from the stdlib and add a test to make sure the
implementation works with CGO_ENABLED=0

providers/darwin/boottime_darwin.go

@@ -15,22 +15,23 @@
 // specific language governing permissions and limitations
 // under the License.
 
-//go:build (amd64 && cgo) || (arm64 && cgo)
-// +build amd64,cgo arm64,cgo
+//go:build amd64 || arm64
+// +build amd64 arm64
 
 package darwin
 
 import (
 	"fmt"
-	"syscall"
 	"time"
+
+	"golang.org/x/sys/unix"
 )
 
 const kernBoottimeMIB = "kern.boottime"
 
 func BootTime() (time.Time, error) {
-	var tv syscall.Timeval
-	if err := sysctlByName(kernBoottimeMIB, &tv); err != nil {
+	tv, err := unix.SysctlTimeval(kernBoottimeMIB)
+	if err != nil {
 		return time.Time{}, fmt.Errorf("failed to get host uptime: %w", err)
 	}
 

providers/darwin/boottime_test.go

@@ -0,0 +1,32 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package darwin
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBoottime(t *testing.T) {
+	bt, err := BootTime()
+	assert.NoError(t, err)
+
+	t.Logf(bt.Format(time.RFC1123))
+}