This looks like an invalid path specified in one of the commands, rather than an incompatibility with mbed. We would advise double-checking every modification to Makefile you made just before this problem started occurring. If you are not sure, please try following the tutorial from the beginning and double-checking that the projects build successfully after each step. Once you locate the step that breaks the build, please double-check the edits made in this step.
If you don’t understand the meaning or role of some edits/custom commands, let us know and we will update the tutorial explaining them in more detail.