[tomjakubowski]

I don't think this problem is limited to system headers. Something as innocent as #include "foo/bar.h" can be affected by this if you pass -I with at least two unique paths to the compiler.

[tedunangst]

ok, sure, I revise my answer to don't shadow any header.

[tomjakubowski]

Easier said than done, especially integrating over the lifetime of a years-long project with many ever-changing dependencies :-)