Make sure the library compiles for windows

systemd sockets are not applicable for windows. However compilation
should not fail on windows

anyhttp.go

@@ -13,7 +13,6 @@ import (
 	"strconv"
 	"strings"
 	"sync"
-	"syscall"
 	"time"
 
 	"go.balki.me/anyhttp/idle"
@@ -150,16 +149,6 @@ func (u *UnixSocketConfig) GetListener() (net.Listener, error) {
 // StartFD is the starting file descriptor number
 const StartFD = 3
 
-func makeFdListener(fd int, name string) (net.Listener, error) {
-	fdFile := os.NewFile(uintptr(fd), name)
-	l, err := net.FileListener(fdFile)
-	if err != nil {
-		return nil, err
-	}
-	syscall.CloseOnExec(fd)
-	return l, nil
-}
-
 // GetListener returns the FileListener created with socketed activated fd
 func (s *SysdConfig) GetListener() (net.Listener, error) {
 

fd_unix.go

@@ -0,0 +1,19 @@
+//go:build unix
+
+package anyhttp
+
+import (
+	"net"
+	"os"
+	"syscall"
+)
+
+func makeFdListener(fd int, name string) (net.Listener, error) {
+	fdFile := os.NewFile(uintptr(fd), name)
+	l, err := net.FileListener(fdFile)
+	if err != nil {
+		return nil, err
+	}
+	syscall.CloseOnExec(fd)
+	return l, nil
+}

fd_windows.go

@@ -0,0 +1,10 @@
+package anyhttp
+
+import (
+	"errors"
+	"net"
+)
+
+func makeFdListener(fd int, name string) (net.Listener, error) {
+	return nil, errors.New("windows not supported")
+}