> makefile and perhaps a configure script

That's a lot to ask for on a non-UNIX system like Windows, and you still also need a C/C++ toolchain (which is typically provided by a Visual Studio installation, which has neither a compatible 'make' nor 'configure').

The next-best alternative would be cmake, but that's a complex boondoggle of its own.

PS: also the toplevel cmdline tool seems to be written in Zig, which might be more convenient than C just because of the Zig stdlib.

It is just a tool so I guess they already know it and it is good enough.

I also know zig build system really well but learning cmake now. I might have used zig too if I had to build something right now

Yeah this feels like it could be packed into a pair of .c source file and header.