Use -idirafter for system includes in translation unit (#64)

Change get_includes() paths from -I to -idirafter so they are
searched after all system headers. This prevents include-path
conflicts when the libclang version differs from the system
compiler (e.g. FreeBSD with clang-19 system headers and
libclang-21), where -I would break #include_next chains.

Co-authored-by: elliejs <elliejs@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: elliejs

bindgen/translation_unit.py

@@ -38,7 +38,7 @@ def parse_tu(
         args.append(f"--sysroot={prefix}")
 
     for inc in get_includes():
-        args.append(f"-I{inc}")
+        args.extend(["-idirafter", inc])
 
     for inc in platform_includes:
         args.append(f"-I{inc}")