Fix build on Windows (#2972)

plugins/inputs/system/linux_sysctl_fs.go

@@ -3,11 +3,13 @@ package system
 import (
 	"bytes"
 	"io/ioutil"
+	"os"
 	"strconv"
 
+	"path"
+
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/inputs"
-	"path"
 )
 
 // https://www.kernel.org/doc/Documentation/sysctl/fs.txt
@@ -80,6 +82,14 @@ func (sfs *SysctlFS) Gather(acc telegraf.Accumulator) error {
 	return nil
 }
 
+func GetHostProc() string {
+	procPath := "/proc"
+	if os.Getenv("HOST_PROC") != "" {
+		procPath = os.Getenv("HOST_PROC")
+	}
+	return procPath
+}
+
 func init() {
 
 	inputs.Add("linux_sysctl_fs", func() telegraf.Input {