compliation fails on OpenBSD 7.3 / Python 3.10

[neonknight]

Environment: fresh installation of OpenBSD 7.3 with Python 3.10 and py3-pip (23.0.1). Created a blank venv with python3 -m venv pylzmaenv; cd pylzmaenv; . bin/activate
Compilation requires malloc.h to which the C compiler needs to be pointed using C_INCLUDE_PATH. Without this variable definition compilation would abort due to missing malloc.h:

export C_INCLUDE_PATH=/usr/include/sys
pip install pylzma                     
Collecting pylzma
  Using cached pylzma-0.5.0.tar.gz (4.2 MB)
  Preparing metadata (setup.py) ... done
Installing collected packages: pylzma
  DEPRECATION: pylzma is being installed using the legacy 'setup.py install' method, because it does not have a 'pyproject.toml' and the 'wheel' package is not installed. pip 23.1 will enforce this behaviour change. A possible replacement is to enable the '--use-pep517' option. Discussion can be found at https://github.com/pypa/pip/issues/8559
  Running setup.py install for pylzma ... error
  error: subprocess-exited-with-error
  
  × Running setup.py install for pylzma did not run successfully.
  │ exit code: 1
  ╰─> [40 lines of output]
      running install
      /root/pyzsdtenv/lib/python3.10/site-packages/setuptools/command/install.py:34: SetuptoolsDeprecationWarning: setup.py install is deprecated. Use build and pip and other standards-based tools.
        warnings.warn(
      running build
      running build_py
      creating build
      creating build/lib.openbsd-7.3-amd64-cpython-310
      copying py7zlib.py -> build/lib.openbsd-7.3-amd64-cpython-310
      running build_ext
      /tmp/pip-install-4ntag9pg/pylzma_657d4583be2344baa09c051d493ca817/setup.py:105: UnsupportedPlatformWarning: Multithreading is not supported on the platform "openbsd7",
      please contact mail@joachim-bauch.de for more informations.
        warn("""\
      building 'pylzma' extension
      creating build/temp.openbsd-7.3-amd64-cpython-310
      creating build/temp.openbsd-7.3-amd64-cpython-310/src
      creating build/temp.openbsd-7.3-amd64-cpython-310/src/compat
      creating build/temp.openbsd-7.3-amd64-cpython-310/src/pylzma
      creating build/temp.openbsd-7.3-amd64-cpython-310/src/sdk
      creating build/temp.openbsd-7.3-amd64-cpython-310/src/sdk/C
      cc -pthread -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -O2 -pipe -g -fPIC -O2 -pipe -g -O2 -pipe -g -fPIC -DPY_SSIZE_T_CLEAN=1 -DWITH_COMPAT=1 -DPYLZMA_VERSION=0.5.0 -D_7ZIP_ST=1 -Isrc/sdk/C -I/root/pyzsdtenv/include -I/usr/local/include/python3.10 -c src/compat/LzmaCompatDecode.c -o build/temp.openbsd-7.3-amd64-cpython-310/src/compat/LzmaCompatDecode.o
      cc -pthread -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -O2 -pipe -g -fPIC -O2 -pipe -g -O2 -pipe -g -fPIC -DPY_SSIZE_T_CLEAN=1 -DWITH_COMPAT=1 -DPYLZMA_VERSION=0.5.0 -D_7ZIP_ST=1 -Isrc/sdk/C -I/root/pyzsdtenv/include -I/usr/local/include/python3.10 -c src/pylzma/pylzma.c -o build/temp.openbsd-7.3-amd64-cpython-310/src/pylzma/pylzma.o
      In file included from src/pylzma/pylzma.c:26:
      In file included from /usr/local/include/python3.10/Python.h:122:
      /usr/local/include/python3.10/pythread.h:136:5: error: "Require native threads. See https://bugs.python.org/issue31370"
      #   error "Require native threads. See https://bugs.python.org/issue31370"
          ^
      /usr/local/include/python3.10/pythread.h:145:5: error: unknown type name 'NATIVE_TSS_KEY_T'
          NATIVE_TSS_KEY_T _key;
          ^
      src/pylzma/pylzma.c:296:5: warning: 'PyEval_InitThreads' is deprecated [-Wdeprecated-declarations]
          PyEval_InitThreads();
          ^
      /usr/local/include/python3.10/ceval.h:122:1: note: 'PyEval_InitThreads' has been explicitly marked deprecated here
      Py_DEPRECATED(3.9) PyAPI_FUNC(void) PyEval_InitThreads(void);
      ^
      /usr/local/include/python3.10/pyport.h:513:54: note: expanded from macro 'Py_DEPRECATED'
      #define Py_DEPRECATED(VERSION_UNUSED) __attribute__((__deprecated__))
                                                           ^
      1 warning and 2 errors generated.
      error: command '/usr/bin/cc' failed with exit code 1
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: legacy-install-failure

× Encountered error while trying to install package.
╰─> pylzma

note: This is an issue with the package mentioned above, not pip.

As I understand pylzma tries to use a thread model no longer supported by newer Python releases on platforms such as OpenBSD.