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

[lh_mouse at 126 dot com via Gcc-bugs]

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

--- Comment #5 from LIU Hao <lh_mouse at 126 dot com> ---
Would you please check whether the libstdc++ DLL in your build directory
contains these symbols?

```
MINGW64 ~
$ nm --defined-only /mingw64/lib/libstdc++.dll.a | grep -F __get_once_call
0000000000000000 I __imp__ZSt19__get_once_callablev
0000000000000000 T _ZSt19__get_once_callablev
0000000000000000 I __imp__ZSt15__get_once_callv
0000000000000000 T _ZSt15__get_once_callv

MINGW64 ~
$ objdump -p /mingw64/bin/libstdc++-6.dll | grep -F __get_once_call
        [5471] +base[5472]  155f _ZSt15__get_once_callv
        [5545] +base[5546]  15a9 _ZSt19__get_once_callablev
```