Add cubeb@62871b2 to Externals/

Includes submodule sanitizers-cmake@f09151b

Externals/cubeb/README.md

@@ -0,0 +1,6 @@
+[![Build Status](https://travis-ci.org/kinetiknz/cubeb.svg?branch=master)](https://travis-ci.org/kinetiknz/cubeb)
+[![Build status](https://ci.appveyor.com/api/projects/status/osv2r0m1j1nt9csr/branch/master?svg=true)](https://ci.appveyor.com/project/kinetiknz/cubeb/branch/master)
+
+See INSTALL.md for build instructions.
+
+Licensed under an ISC-style license.  See LICENSE for details.