Skip C extension build on GraalPy

Author: msimacek

_setup.py

@@ -130,7 +130,7 @@ def build_extension(self, ext):
     except ValueError:
         pass
     ext_modules = []
-elif sys.platform.startswith("java") or sys.platform == "cli" or "PyPy" in sys.version:
+elif sys.platform.startswith("java") or sys.platform == "cli" or sys.implementation.name in ('pypy', 'graalpy'):
     sys.stdout.write(
         """
 *****************************************************\n