Current status for me on Windows: merging the buildsystem branch, installing NDK13b and running cmake_android resulted in the NDK's Clang erroring on not finding various C++ headers, while it was building the Urho PCH.
In file included from D:/Lasse/Programs/urho3d-clean2/Source/Urho3D/Precompiled.
In file included from D:/Lasse/Programs/urho3d-clean2/Source/Urho3D/Container/Ha
In file included from D:/Lasse/Programs/urho3d-clean2/Source/Urho3D/Container/..
0: fatal error: 'cstddef' file not found