Build as a platlib

Author: aostrowski-hbn

Diff for: setup.py

@@ -24,7 +24,7 @@
 
 if use_setuptools:
     try:
-        from setuptools import setup
+        from setuptools import Extension, setup
         from setuptools.command.install import install as _install
         from setuptools.command.build_ext import build_ext as _build_ext
     except ImportError:
@@ -232,7 +232,10 @@ def finalize_options(self):
       url="https://github.com/symengine/symengine.py",
       python_requires='>=3.9,<4',
       zip_safe=False,
-      packages=['symengine', 'symengine.lib', 'symengine.tests'],
+      ext_modules=[
+        Extension(name='symengine.lib', sources=[]),
+        Extension(name='symengine.tests', sources=[])],
+      packages=['symengine'],
       cmdclass = cmdclass,
       classifiers=[
         'License :: OSI Approved :: MIT License',