internal/mobileinit: send iOS logs to ASL

Fixes golang/go#12194

Change-Id: I9ff771336996c19ca43da56e3f8944e79c980a2b
Reviewed-on: https://go-review.googlesource.com/13703
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

internal/mobileinit/mobileinit_ios.go

@@ -0,0 +1,38 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin
+// +build arm arm64
+
+package mobileinit
+
+import (
+	"io"
+	"log"
+	"os"
+	"unsafe"
+)
+
+/*
+#include <asl.h>
+#include <stdlib.h>
+
+void asl_log_wrap(const char *str) {
+	asl_log(NULL, NULL, ASL_LEVEL_NOTICE, str);
+}
+*/
+import "C"
+
+type aslWriter struct{}
+
+func (aslWriter) Write(p []byte) (n int, err error) {
+	cstr := C.CString(string(p))
+	C.asl_log_wrap(cstr)
+	C.free(unsafe.Pointer(cstr))
+	return len(p), nil
+}
+
+func init() {
+	log.SetOutput(io.MultiWriter(os.Stderr, aslWriter{}))
+}