[clangd] Collect missing macro references.

Summary: Semantic highlghting is missing a few macro references.

Reviewers: ilya-biryukov

Subscribers: MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D68458

llvm-svn: 373889