[Bug c++/90126] gcc can not correctly deal with its own preprocessed output

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90126

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
tl;dr the preprocessor should only be used once. You're running it twice on the
same input.