Note about why this isn't vendor_available. am: eda4e913a5

Change-Id: Id9a6da98d21e000e6ef4b9d9a8a4d7c52840a076

Android.bp

@@ -149,6 +149,9 @@ cc_library_static {
     ],
 }
 
+// Not available to vendor modules until libc++ is updated and this library is
+// merged into libc++ proper.
+// https://issuetracker.google.com/147469372
 cc_library_static {
     name: "libc++fs",
     recovery_available: true,