setup: fall back to setuptools setup if distutils isn't available

The setuptools comments around this seems slightly outdated. Setuptools is
improving and distutils is being deprecated, so it should perhaps be the
default. But at least, it is a fair fallback.

setup.py

@@ -112,7 +112,10 b" issetuptools = os.name == 'nt' or 'FORCE"
 if issetuptools:
     from setuptools import setup
 else:
-    from distutils.core import setup
+    try:
+        from distutils.core import setup
+    except ModuleNotFoundError:
+        from setuptools import setup
 from distutils.ccompiler import new_compiler
 from distutils.core import Command, Extension
 from distutils.dist import Distribution