I haven't tried to use the whole setup (with all headers etc) but if I put in my .c file the definition of struct and the ANSI C version of the definition of de

I haven't tried to use the whole setup (with all headers etc) but if I put in my .c file the definition of struct and the ANSI C version of the definition of define_label, struct label *define_label(char* name, int value) { .. then C88 compiles without errors. On the page about the compiler the author of the page writes that he had to fix the standard libraries, but the compiler (C88) is definitely made to work with ANSI C "draft" which matches my experiment. And I surely understand it was "good enough" a solution for you to do what you did.