libclang: How to distinguish project and system includes?

Question

I am using libclang (Python bindings) to parse some C++ code. I need to distinguish includes that resolve to system headers, e.g., #include <algorithm>, from includes that resolve to project-local headers, e.g., #include "my_header.h".

The problem is that I cannot find a way to retrive this information from the libclang AST.

Some thoughts/considerations:

• the information has to be there somewhere, since running clang with -E (only run preprocessor), system includes are marked by appending the flag 3 when they are included. Example:
  # 1 "/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/exception" 1 3
• of course, I could invoke the preprocessor myself and match the results, but this adds overhead and more potential sources for bugs
• simply look for <> vs "" in the tokens of the include statement does not work, as they just determine lookup order.
• checking the beginning of the expanded include file path for sth like /usr/lib/... does not work, since it is not platform independent and the user can add custom "system" directories via -isystem.

I hope you can help me out on this :)