v0.31.0: Undefined symbol "call_once" on FreeBSD 15

first things first: thanks for the great software!

my issue:
installed under python 3.12 via pip on FreeBSD 15.1-p1:

```...
Collecting asyncpg==0.31.0
  Using cached asyncpg-0.31.0-cp312-cp312-freebsd_15_1_release_p1_amd64.whl
Installing collected packages: asyncpg
...
```

results in this:
```...
    import asyncpg
  File "/usr/home/l9/py312/lib/python3.12/site-packages/asyncpg/__init__.py", line 9, in <module>
    from .connection import connect, Connection  # NOQA
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/home/l9/py312/lib/python3.12/site-packages/asyncpg/connection.py", line 25, in <module>
    from . import connect_utils
  File "/usr/home/l9/py312/lib/python3.12/site-packages/asyncpg/connect_utils.py", line 33, in <module>
    from . import protocol
  File "/usr/home/l9/py312/lib/python3.12/site-packages/asyncpg/protocol/__init__.py", line 11, in <module>
    from .protocol import Protocol, NO_TIMEOUT, BUILTIN_TYPE_NAME_MAP
ImportError: /usr/home/l9/py312/lib/python3.12/site-packages/asyncpg/protocol/protocol.cpython-312.so: Undefined symbol "call_once"
```

```% ldd python3.12/site-packages/asyncpg/protocol/protocol.cpython-312.so
python3.12/site-packages/asyncpg/protocol/protocol.cpython-312.so:
	libthr.so.3 => /lib/libthr.so.3 (0x103df0c5a000)
	libc.so.7 => /lib/libc.so.7 (0x103df255f000)
	libsys.so.7 => /lib/libsys.so.7 (0x103df2bb6000)
```

None of the three libs contains the `call_once` symbol.
Some link error / missconfiguration?!

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