[pjmlp]

The only way to do this fully automatic is to integrate a partial C compiler, able to understand the pre-processor and all types of declarations.

[dbaupp]

There was/is a plan to use clang to help with this.

(In fact, rustc used to build clang as well as LLVM, but this was disabled since it wasn't being used (yet).)

[pjmlp]

This is the approach also taken by DStep for D.

https://github.com/jacob-carlborg/dstep