Cannot express depenencies from llvm-libc-macros to llvm-libc-types

This is because the macros subfolder is added before "types". And our target-adding macros depend on require that the dependencies already exist.

Unsure how to resolve this. Cmake normally does not require targets to be added in dependency order, but I believe we have a lot of infrastructure built around this expectation.

Start by tracing how the llvm-libc-macros subfolder is added before llvm-libc-types and how the target-adding macros require existing dependencies. Read the surrounding CMake infrastructure to determine whether dependency order can be removed or must be supported; done means macros can depend on types without breaking target creation.

Written by the indexing model from the issue text.