libmf | LIBMF is a library for large-scale sparse matrix | Machine Learning library

By passing -DANDROID_STL=c++_shared to the CMake invocation you explicitly asked for the shared runtime as opposed to the default runtime.

As explained in the documentation, the rules are simple:

1. if all your native code is in a single library, use the static libc++ (the default) such that unused code can be removed and you have the smallest possible application package.
2. As soon as you include an extra library – either because you include a precompiled library from somewhere else or you include an Android AAR file that happens to include native code – you must switch to the shared runtime.

The rationale for the rules is simple: the C++ runtime has certain global data structures that must be initialized once and must only exist once in memory. If you were accidentally to load two libraries that both link the C++ runtime statically, you have (for instance) two conflicting memory allocators. This will result in crashes when you free or delete memory allocated by the other library, or if you pass a C++ STL object like std::string across library boundaries.

For completeness, in older NDKs libstdc++ (the GNU C++ runtime) was also included in the NDK, but as of NDK r18 that is no longer the case.