[clang] [Clang] suggest headers on undeclared errors (PR #140247)

[Jongmyeong Choi via cfe-commits]

jongmyeong-choi wrote:

Thanks for all your reviews. I learned a lot from your comments. I'll try to rewrite it from scratch, but honestly, it'll take me a while to figure out the TableGen structure. If anyone wants to make a change to this topic, please feel free to jump in.

https://github.com/llvm/llvm-project/pull/140247