builder: fix compiling with buildkit on windows and integration tests

Signed-off-by: Tibor Vass <tibor@docker.com>

builder/builder-next/controller.go

@@ -15,7 +15,6 @@ import (
 	"github.com/moby/buildkit/cache/metadata"
 	"github.com/moby/buildkit/cache/remotecache"
 	"github.com/moby/buildkit/control"
-	"github.com/moby/buildkit/executor/runcexecutor"
 	"github.com/moby/buildkit/exporter"
 	"github.com/moby/buildkit/frontend"
 	"github.com/moby/buildkit/frontend/dockerfile"
@@ -89,10 +88,7 @@ func newController(rt http.RoundTripper, opt Opt) (*control.Controller, error) {
 		return nil, err
 	}
 
-	exec, err := runcexecutor.New(runcexecutor.Opt{
-		Root:              filepath.Join(root, "executor"),
-		CommandCandidates: []string{"docker-runc", "runc"},
-	})
+	exec, err := newExecutor(root)
 	if err != nil {
 		return nil, err
 	}

builder/builder-next/executor_unix.go

@@ -0,0 +1,17 @@
+// +build !windows
+
+package buildkit
+
+import (
+	"path/filepath"
+
+	"github.com/moby/buildkit/executor"
+	"github.com/moby/buildkit/executor/runcexecutor"
+)
+
+func newExecutor(root string) (executor.Executor, error) {
+	return runcexecutor.New(runcexecutor.Opt{
+		Root:              filepath.Join(root, "executor"),
+		CommandCandidates: []string{"docker-runc", "runc"},
+	})
+}

builder/builder-next/executor_windows.go

@@ -0,0 +1,11 @@
+package buildkit
+
+import (
+	"errors"
+
+	"github.com/moby/buildkit/executor"
+)
+
+func newExecutor(_ string) (executor.Executor, error) {
+	return nil, errors.New("buildkit executor not implemented for windows")
+}