[Bug libstdc++/68739] FAIL: 30_threads/call_once/constexpr.cc (test for excess errors)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68739

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
((void *)0 + 1) is also technically ill-formed, but G++ accepts it (Bug 60760).