Buildtag out unix commands for common OS files

Unix only code crept into shared portions of the machine codebase,
preventing builds on Windows. Move them into unix-only files.

[NO NEW TESTS NEEDED]

Signed-off-by: Ashley Cui <acui@redhat.com>

pkg/machine/qemu/machine.go

@@ -28,7 +28,6 @@ import (
 	"github.com/containers/storage/pkg/lockfile"
 	"github.com/digitalocean/go-qemu/qmp"
 	"github.com/sirupsen/logrus"
-	"golang.org/x/sys/unix"
 )
 
 var (
@@ -589,15 +588,7 @@ func (v *MachineVM) qemuPid() (int, error) {
 		logrus.Warnf("Reading QEMU pidfile: %v", err)
 		return -1, nil
 	}
-
-	if err := unix.Kill(pid, 0); err != nil {
-		if err == unix.ESRCH {
-			return -1, nil
-		}
-		return -1, fmt.Errorf("pinging QEMU process: %w", err)
-	}
-
-	return pid, nil
+	return findProcess(pid)
 }
 
 // Start executes the qemu command line and forks it
@@ -970,7 +961,7 @@ func (v *MachineVM) Stop(_ string, _ machine.StopOptions) error {
 		return stopErr
 	}
 
-	if err := unix.Kill(qemuPid, unix.SIGKILL); err != nil {
+	if err := sigKill(qemuPid); err != nil {
 		if stopErr == nil {
 			return err
 		}

pkg/machine/qemu/machine_unix.go

@@ -43,3 +43,17 @@ func extractTargetPath(paths []string) string {
 	}
 	return paths[0]
 }
+
+func sigKill(pid int) error {
+	return unix.Kill(pid, unix.SIGKILL)
+}
+
+func findProcess(pid int) (int, error) {
+	if err := unix.Kill(pid, 0); err != nil {
+		if err == unix.ESRCH {
+			return -1, nil
+		}
+		return -1, fmt.Errorf("pinging QEMU process: %w", err)
+	}
+	return pid, nil
+}

pkg/machine/qemu/machine_windows.go

@@ -50,3 +50,11 @@ func extractTargetPath(paths []string) string {
 	dedup := regexp.MustCompile(`//+`)
 	return dedup.ReplaceAllLiteralString("/"+target, "/")
 }
+
+func sigKill(pid int) error {
+	return nil
+}
+
+func findProcess(pid int) (int, error) {
+	return -1, nil
+}