The existing ctests cannot be simply used in Android tests because
everything is compiled as standalone executable with `main()` function.
Since Android 11+ does not support standalone executables, those test
`main()` functions are converted as unique functions and then picked up
in this test's native-lib CMakeLists.txt.
Since those tests depend on libfluidsynth internals, we cannot simply
link with libfluidsynth.so. We instead compile the library with OBJ files.
