Disable C tokenizer building on PyPy (fixes #341)

CHANGELOG

@@ -1,6 +1,6 @@
 v0.7.2 (unreleased):
 
-- ...
+- Fix building on non-CPython implementations like PyPy. (#341)
 
 v0.7.1 (released June 30, 2025):
 

docs/changelog.rst

@@ -7,7 +7,8 @@ v0.7.2
 Unreleased
 (`changes <https://github.com/earwig/mwparserfromhell/compare/v0.7.1...main>`__):
 
-- ...
+- Fix building on non-CPython implementations like PyPy.
+  (`#341 <https://github.com/earwig/mwparserfromhell/issues/341>`_)
 
 v0.7.1
 ------

setup.py

@@ -24,6 +24,7 @@ from __future__ import annotations
 
 import glob
 import os
+import platform
 import sys
 from enum import Enum
 
@@ -63,8 +64,10 @@ elif "WITHOUT_EXTENSION" in os.environ:
             f"Unknown value for $WITHOUT_EXTENSION; should be '1', or '0', "
             f"but found {value!r}"
         )
-else:
+elif platform.python_implementation() == "CPython":
     use_extension = UseExtension.REQUIRED
+else:
+    use_extension = UseExtension.IGNORED
 
 if use_extension == UseExtension.IGNORED:
     ext_modules = []