The site's intention is nice in theory but not really feasible in practice. To get an OS running on a computer, you need binaries anyways, so having some more binaries for programming languages isn't really that bad. There also isn't even an easily bootstrappable C compiler afaik.
They've gotten really far, though. Jan's Mes can compile tcc which can compile an older version of GCC. They just need enough of a C compiler to compile MesC.
https://gitlab.com/janneke/mes
"To get an OS running on a computer, you need binaries anyways, so having some more binaries for programming languages isn't really that bad. "
That's what I keep telling folks obsessed with this. If they insist on non-binary solutions, David A. Wheeler and I talked about using scripting languages that come with the system. I was looking at Perl with him mentioning bash. I added bash, Tcl, and awk compilers to the bootstrapping collection just in case. That's on top of the usual like Forth, LISP, or META II. People put some small, C compilers in there like you were talking about.