[Bug bootstrap/89864] [9 regression] gcc fails to build/bootstrap with XCode 10.2

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89864

--- Comment #60 from Jonathan Wakely <redi at gcc dot gnu.org> ---
PR 81797 was the relevant bug, which apparently is still present for darwin
when using the buggy new APFS filesystem.