Don't try to compile CPLB on darwin

The unix build tag includes darwin, but CPLB only compiles on Linux. Use
the linux build tag for the implementation instead, and use the current
windows stub for anything that isn't linux.

Signed-off-by: Tom Wieczorek <[email protected]>

pkg/component/controller/cplb_unix.go → pkg/component/controller/cplb_linux.go

@@ -1,5 +1,3 @@
-//go:build unix
-
 /*
 Copyright 2024 k0s authors
 

pkg/component/controller/cplb_windows.go → pkg/component/controller/cplb_other.go

@@ -1,3 +1,5 @@
+//go:build !linux
+
 /*
 Copyright 2024 k0s authors
 
@@ -19,6 +21,8 @@ package controller
 import (
 	"context"
 	"errors"
+	"fmt"
+	"runtime"
 
 	k0sAPI "github.com/k0sproject/k0s/pkg/apis/k0s/v1beta1"
 	"github.com/k0sproject/k0s/pkg/config"
@@ -35,14 +39,14 @@ type Keepalived struct {
 	KubeConfigPath  string
 }
 
-func (k *Keepalived) Init(_ context.Context) error {
-	return errors.New("CPLB is not supported on Windows")
+func (k *Keepalived) Init(context.Context) error {
+	return fmt.Errorf("%w: CPLB is not supported on %s", errors.ErrUnsupported, runtime.GOOS)
 }
 
-func (k *Keepalived) Start(_ context.Context) error {
-	return errors.New("CPLB is not supported on Windows")
+func (k *Keepalived) Start(context.Context) error {
+	return fmt.Errorf("%w: CPLB is not supported on %s", errors.ErrUnsupported, runtime.GOOS)
 }
 
 func (k *Keepalived) Stop() error {
-	return errors.New("CPLB is not supported on Windows")
+	return fmt.Errorf("%w: CPLB is not supported on %s", errors.ErrUnsupported, runtime.GOOS)
 }