89b1d5c818a33440c0c497aa78721fb9b0af35a5 depends: Fix `zeromq` build on OpenBSD (Hennadii Stepanov)
Pull request description:
On the master branch @ 66e82dc90c598c9c42ff980693ef5367a845e1d0, the `zeromq` package fails to build on OpenBSD 7.5:
```
[ 19%] Building CXX object CMakeFiles/objects.dir/src/io_thread.cpp.o
/home/hebasto/bitcoin/depends/work/build/amd64-unknown-openbsd7.5/zeromq/4.3.5-df5b1b9f936/src/io_thread.cpp:14:22: error: static_cast from 'std::nullptr_t' to 'poller_t::handle_t' (aka 'int') is not allowed
_mailbox_handle (static_cast<poller_t::handle_t> (NULL))
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
```
This [regression](https://github.com/bitcoin/bitcoin/pull/29723#issuecomment-2261513105) was overlooked by me in https://github.com/bitcoin/bitcoin/pull/29723.
This PR fixes the issue by backporting an upstream commit from https://github.com/zeromq/libzmq/pull/4659.
ACKs for top commit:
theStack:
tACK 89b1d5c818a33440c0c497aa78721fb9b0af35a5
Tree-SHA512: 48d22ea99dfd44c5adf858c74e64082390da27b8ccad8c0d5a91d4dabfa3d12267cef98e4bb8c088e4cd0ec477c242cb1d47aace5c88cd86f796715bba957ed8
