BUG: "No module named cython" when building 26.0.0+ with Pyston 2.3.5

### This is a pyzmq bug

- [X] This is a pyzmq-specific bug, not an issue of zmq socket behavior. Don't worry if you're not sure! We'll figure it out together.

### What pyzmq version?

26.0.0+

### What libzmq version?

4.3.4

### Python version (and how it was installed)

pyston-2.3.5 installed via pyenv

### OS

Ubuntu 22.04

### What happened?

When updating pyzmq from version 25.1.2 I got an error.

### Code to reproduce bug

```python
1. Install pyston-2.3.5 from pyenv

2. Make a virtualenv

3. Try to install pyzmq
```


### Traceback, if applicable

```shell
(more can be provided on request)

...

  [103/109] Building CXX object _deps/bundled_libzmq-build/CMakeFiles/objects.dir/src/tipc_connecter.cpp.o

  [104/109] Building CXX object _deps/bundled_libzmq-build/CMakeFiles/objects.dir/src/udp_engine.cpp.o

  [105/109] Building CXX object _deps/bundled_libzmq-build/CMakeFiles/objects.dir/src/socket_base.cpp.o

  [106/109] Linking CXX static library _deps/bundled_libzmq-build/lib/libzmq.a

  [107/109] Generating _src/_zmq.c

  FAILED: _src/_zmq.c /tmp/tmpd9xa1398/build/_src/_zmq.c

  cd /tmp/tmpd9xa1398/build && /home/davidlaw/.pyenv/versions/pyston-2.3.5/envs/pyzmq-test-pyston-2.3.5/bin/python -mcython --3str --output-file /tmp/tmpd9xa1398/build/_src/_zmq.c --module-name zmq.backend.cython._zmq /tmp/pip-install-m1z8ag2s/pyzmq_22e735db494c49e7b0d28815b1ad745c/zmq/backend/cython/_zmq.py

  /home/davidlaw/.pyenv/versions/pyston-2.3.5/envs/pyzmq-test-pyston-2.3.5/bin/python: No module named cython

  ninja: build stopped: subcommand failed.



  *** CMake build failed

  error: subprocess-exited-with-error

  

  × Building wheel for pyzmq (pyproject.toml) did not run successfully.

  │ exit code: 1

  ╰─> See above for output.

  

  note: This error originates from a subprocess, and is likely not a problem with pip.

  full command: /home/davidlaw/.pyenv/versions/pyston-2.3.5/envs/pyzmq-test-pyston-2.3.5/bin/python /home/davidlaw/.pyenv/versions/pyston-2.3.5/envs/pyzmq-test-pyston-2.3.5/lib/python3.8-pyston2.3/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py build_wheel /tmp/tmpsj5fhcnz

  cwd: /tmp/pip-install-m1z8ag2s/pyzmq_22e735db494c49e7b0d28815b1ad745c

  Building wheel for pyzmq (pyproject.toml) ... error

  ERROR: Failed building wheel for pyzmq

Failed to build pyzmq

ERROR: Could not build wheels for pyzmq, which is required to install pyproject.toml-based projects

Exception information:

Traceback (most recent call last):

  File "/home/davidlaw/.pyenv/versions/pyston-2.3.5/envs/pyzmq-test-pyston-2.3.5/lib/python3.8-pyston2.3/site-packages/pip/_internal/cli/base_command.py", line 180, in exc_logging_wrapper

    status = run_func(*args)

  File "/home/davidlaw/.pyenv/versions/pyston-2.3.5/envs/pyzmq-test-pyston-2.3.5/lib/python3.8-pyston2.3/site-packages/pip/_internal/cli/req_command.py", line 245, in wrapper

    return func(self, options, args)

  File "/home/davidlaw/.pyenv/versions/pyston-2.3.5/envs/pyzmq-test-pyston-2.3.5/lib/python3.8-pyston2.3/site-packages/pip/_internal/commands/install.py", line 429, in run

    raise InstallationError(

pip._internal.exceptions.InstallationError: Could not build wheels for pyzmq, which is required to install pyproject.toml-based projects

Remote version of pip: 24.0

Local version of pip:  24.0

Was pip installed by pip? True

Removed build tracker: '/tmp/pip-build-tracker-ih8jssr0'

```
```


### More info

I have tried installing in a clean virtualenv, and again after manually installing Cython. I got the same result both times.



25.1.2 installs fine.

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