Add license header

src/main/java/com/google/devtools/build/lib/skyframe/toolchains/ToolchainContextUtil.java

@@ -1,3 +1,16 @@
+// Copyright 2024 The Bazel Authors. All rights reserved.
+//
+// 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.
 package com.google.devtools.build.lib.skyframe.toolchains;
 
 import com.google.common.collect.ImmutableSet;