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)

setup.py

@@ -6,7 +6,19 @@
 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,
+        DistutilsExecError as ExecError,
+        DistutilsPlatformError as PlatformError,
+    )
 
 
 # Those are needed to build _hton for windows