Code generation successful, but now .so file is created

I'm using the Simulink Coder to generate a shared library from a model. I've done this several time before, and I think I have the same settings as then. However, even though the generation is successful I don't get a .so file. I do get a makefile, but when I tried to run that using gmake in a terminal, it failed (without giving much in terms of clues).

What could be the cause of this issue, and how can I debug the problem?