GDSL is written in C++ with use of STL, templates and lambdas, so it's 2600 lines of such C++ source code. There is no self-hosting: neither the LISP compiler nor the C compiler can compile itself. No operating system is implemented, the word kernel in the title means something else.
FYI Here is a 700-line subset-of-C compiler which can compile itself: https://github.com/valdanylchuk/xcc700 . FYI The linker and the libc are not included.