There must be like a 1000 examples of c compilers in git hub alone. No idea why building LLM building one is impressive. It's right there in the training data.
No. Starting in a sandbox given only the C specification and assembly code specification build a gcc equivalent (maintainability and performance) from the ground up.
https://github.com/anthropics/claudes-c-compiler
Also I dunno why you should be impressed by this - gcc isn't anything near eg navier stokes