I don't think it's so clear-cut. The C spec I found is 4MB and the tcc compiler source code is 1.8MB. It might need some more code to be fully compliant, but it may still be smaller than 4MB. I think the main reason why code bases are much larger is because they contain stuff not covered by the spec (optimization, vendor-specific stuff, etc etc).

Personally I'd rather write a compiler than a specification, but to each their own.