Ah yes, that’s the same issue @mseri pointed. We need to do something about this in dune. In the meantime, the simplest solution is to put the call to make and the various files copy in a shell script rather than use the DSL. For instance, you can write a shell script containing:
make -C c
cp c/libxxx.a libmylib_c_stubs.a
cp c/libxxx.so dllmylib_c_stubs.so
and call this shell script.