I developed something for C that just works in github markdown files, but without place holders. It just parses all the fragments, possibly from multiple files,

I developed something for C that just works in github markdown files, but without place holders. It just parses all the fragments, possibly from multiple files, and puts them in an order to be compiled. It does automatically generate forward declarations for functions. The generated C output does contain #line lines. I used this in the past years for AoC.