[Bug preprocessor/108101] "#pragma once" causes other files not be included

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108101

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Iirc pragma once uses a hash of the content and that is what is going on here.
That or the underlying file system is using some inode being the same and copy
on write.