It doesn't rely on gcc. Any C compiler will do. The rest is there to build it on " Linux, OSX, and Windows using MSYS2 and mingw32". Indeed for cross-compilation, as it won't run on CP/M.

> apparently known as being the default toolchain for Minix 1 and 2.

That is not very surprising since Tannenbaum is a professor there and cowrote wrote the ACK and wrote Minix.

ACK used to be self-hosting. Of course, standard Unix utilities like sh and make are required. I still use one of those versions.