Android build

Some changes on the android toolchain file to make new c++11 features available, the android build now uses c++_shared (LLVM) version of the NDK.
Yes, I totally agree and that's what I also wanted, I tried to figure out for a solution. To do this we should either add more parameters for cached variable to the cmake command or remove the cached variable we are using in the android.toolchain.cmake since it's the first loaded since the -DCMAKE_TOOLCHAIN_FILE loads the file at the very first step (the include in the android.cmake is misleading about and should be removed in this case).