Merge pull request docker#1863 from tiborvass/buildx-backports

buildx backports: BUILDKIT_PROGRESS env + build --platform local

cli/command/image/build_buildkit.go

@@ -14,6 +14,7 @@ import (
 	"strings"
 
 	"github.com/containerd/console"
+	"github.com/containerd/containerd/platforms"
 	"github.com/docker/cli/cli"
 	"github.com/docker/cli/cli/command"
 	"github.com/docker/cli/cli/command/image/build"
@@ -215,6 +216,14 @@ func runBuildBuildKit(dockerCli command.Cli, options buildOptions) error {
 		})
 	}
 
+	if v := os.Getenv("BUILDKIT_PROGRESS"); v != "" && options.progress == "auto" {
+		options.progress = v
+	}
+
+	if strings.EqualFold(options.platform, "local") {
+		options.platform = platforms.DefaultString()
+	}
+
 	eg.Go(func() error {
 		defer func() { // make sure the Status ends cleanly on build errors
 			s.Close()