Add empty Android.mk to prevent recursion.

Bug: 72661763
Test: find . -name 'Android.mk'
Change-Id: I8373f1433561bd9ae4652dc58bd2fbcb8e7d721e
diff --git a/Android.mk b/Android.mk
new file mode 100644
index 0000000..3622a71
--- /dev/null
+++ b/Android.mk
@@ -0,0 +1,5 @@
+# Intentially empty, to prevent recursion
+#
+# There is an NDK test under modules/audio_procesing/test. The NDK build system
+# uses Android.mk files too, but they're not compatible with the Platform
+# Android.mk files.