Copy prebuilts/ndk/r25/Android.mk into r26

This file is needed to prevent master-plus-llvm's Kati build from
reading the Android.mk files in sources/android/* and (for example)
defining a duplicate "cpufeatures" modules.

Bug: http://b/175635923
Test: treehugger
Change-Id: If4a7ec3f2a53882903bce381a50c79f7b742b9bf
diff --git a/Android.mk b/Android.mk
new file mode 100644
index 0000000..d98dc99
--- /dev/null
+++ b/Android.mk
@@ -0,0 +1,17 @@
+#
+# Copyright (C) 2022 The Android Open Source Project
+#
+# 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.
+#
+
+# Intentionally empty to prevent subdir Android.mk loading