I assume the essentially universal use of `FetchContent` is to download a third party package. In such a case, it serves the role of a "system" header: compiler warnings aren't useful. It seems like in this case the `INTERFACE_INCLUDE_DIRECTORIES` specified by the package should be marked as a system include directory. If this is not the correct default, perhaps the `SYSTEM` keyword could be included to `FetchContent_Declare` to specify that this is desired.