Out of curiosity, I took nafraf's files from his svn repo (loader/sx170is and platform/sx170is), copied them into a fresh trunk tree, executed:
make rebuild-stubs PLATFORM=sx170is PLATFORMSUB=100a
make run-code-gen PLATFORM=sx170is PLATFORMSUB=100a
make fir PLATFORM=sx170is PLATFORMSUB=100a
Build was successful.
Same happened for 101a.
PRIMARY.BIN files were at their right place (this is needed for rebuild-stubs and run-code-gen).
This was on a Linux system, but I think you should get the same on Windows. I think you get a proper command prompt with correct PATH if you click the black icon in the lower right part of the CHDK Shell window. You may need to use gmake, not make. The trunk tree should be unaltered of course.