Fix RTD doc compilation

aio-libs#810 imports errors from
`setuptools` instead of `distutils`

This is available only starting from `setuptools` v59.0.0
(pypa/setuptools#2858) but RTD currently
defaults to v58.2.0
(https://docs.readthedocs.io/en/stable/builds.html#python)

requirements-docs.txt

@@ -1,4 +1,5 @@
 -r requirements-cython.txt
+setuptools>=59.0.0 # Install a newer setuptools on rtd, which defaults to pre-https://github.com/pypa/setuptools/pull/2858
 Sphinx==4.3.0
 sphinxcontrib-asyncio==0.3.0
 sphinxcontrib-spelling==7.2.1

setup.py

@@ -6,7 +6,15 @@
 from setuptools import Extension, setup
 from setuptools.command.bdist_rpm import bdist_rpm as _bdist_rpm
 from setuptools.command.build_ext import build_ext
-from setuptools.errors import CCompilerError, ExecError, PlatformError
+
+try:
+    from setuptools.errors import CCompilerError, ExecError, PlatformError
+except ImportError:
+    # RTD workaround until it ships setuptools>=v59.0.0
+    # See:
+    # - https://github.com/pypa/setuptools/pull/2858
+    # - https://docs.readthedocs.io/en/stable/builds.html#python
+    from distutils.errors import CCompilerError, ExecError, PlatformError
 
 
 # Those are needed to build _hton for windows