[Bug bootstrap/82091] [5 only] Build failure on macOS 10.13 with Xcode 9

[juergen.reuter at desy dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82091

--- Comment #6 from Jürgen Reuter <juergen.reuter at desy dot de> ---
I do see this error now also with the trunk version [r260425] under Darwin 17.5
with Xcode 9.3.1.