[Bug pch/108732] Pre-compiled headers cannot be output to /dev/null

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108732

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
>it always worked with previous GCC versions

Not really. Just by accident really.

See r12-5320-ge4641191287ca6

Basically it means mmap failed on the file; well because mmap does not work on
/dev/null .