Unversion NDK stub libraries.

The system versions of these libraries aren't versioned yet.

Bug: https://github.com/android-ndk/ndk/issues/278
Test: make ndk
Change-Id: If912ebc82a846fb4ce0bb1b7c4e3221e3b52a3c7
diff --git a/Android.bp b/Android.bp
index 5085cda..3928720 100644
--- a/Android.bp
+++ b/Android.bp
@@ -24,6 +24,7 @@
     name: "libOpenMAXAL.ndk",
     symbol_file: "libOpenMAXAL.map.txt",
     first_version: "14",
+    unversioned_until: "current",
 }
 
 ndk_headers {
@@ -38,4 +39,5 @@
     name: "libOpenSLES.ndk",
     symbol_file: "libOpenSLES.map.txt",
     first_version: "9",
+    unversioned_until: "current",
 }