[Bug libstdc++/123908] [16 regression] Undefined reference to std::__get_once_call()

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123908

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think the symbols are still missing. Comment 8 is saying that the patch from
comment 7 did not cause a build failure, so confirming that the macros are set
correctly. But the symbols are still not exported from the dll.