A parser/compiler could obviously be improved with an LLM (AI!) to suggest improvements to invalid input. That is actually a super good use case of LLM/AI.

Having clang/gcc, or any other parser, implement that is of course impossible, they are too conservative and would rather die than to implement modern helpful tools.

You're presumably using an LLM to drive the compiler, and your LLM should be just as capable of reading the compiler's error message and fixing the problem. So why double the work?