[Bug libffi/65726] [5/6 Regression] libffi fails to build when not bootstrapping: configure: error: C++ preprocessor "/lib/cpp" fails sanity check

[gerald at pfeifer dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65726

--- Comment #8 from Gerald Pfeifer <gerald at pfeifer dot com> ---
This one fixes the problem in all my tests.