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

[jakub at gcc dot gnu.org]

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

--- Comment #48 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Perhaps that redefinition of _Atomic should be guarded with
#if (__STDC_VERSION__ < 201112L) || defined(__cplusplus)
or so, so that for C -std=c11 you still get _Atomic?