vendor: update buildkit to v0.18.0-rc1

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp/wrap.go

@@ -1,16 +1,5 @@
 // Copyright The OpenTelemetry Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
+// SPDX-License-Identifier: Apache-2.0
 
 package otelhttp // import "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 
@@ -18,6 +7,7 @@ import (
 	"context"
 	"io"
 	"net/http"
+	"sync/atomic"
 
 	"go.opentelemetry.io/otel/propagation"
 )
@@ -30,14 +20,14 @@ type bodyWrapper struct {
 	io.ReadCloser
 	record func(n int64) // must not be nil
 
-	read int64
+	read atomic.Int64
 	err  error
 }
 
 func (w *bodyWrapper) Read(b []byte) (int, error) {
 	n, err := w.ReadCloser.Read(b)
 	n1 := int64(n)
-	w.read += n1
+	w.read.Add(n1)
 	w.err = err
 	w.record(n1)
 	return n, err
@@ -97,3 +87,13 @@ func (w *respWriterWrapper) WriteHeader(statusCode int) {
 	}
 	w.ResponseWriter.WriteHeader(statusCode)
 }
+
+func (w *respWriterWrapper) Flush() {
+	if !w.wroteHeader {
+		w.WriteHeader(http.StatusOK)
+	}
+
+	if f, ok := w.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	}
+}