Fix some usage of deprecated `imp` module

changelog.d/479.change.rst

+Remove some usage of the deprecated ``imp`` module.

setuptools/command/build_ext.py

 import os
 import sys
 import itertools
-import imp
 from distutils.command.build_ext import build_ext as _du_build_ext
 from distutils.file_util import copy_file
 from distutils.ccompiler import new_compiler
@@ -12,6 +11,13 @@ from distutils import log
 from setuptools.extension import Library
 from setuptools.extern import six
 
+if six.PY2:
+    import imp
+
+    EXTENSION_SUFFIXES = [s for s, _, tp in imp.get_suffixes() if tp == imp.C_EXTENSION]
+else:
+    from importlib.machinery import EXTENSION_SUFFIXES
+
 try:
     # Attempt to use Cython for building extensions, if available
     from Cython.Distutils.build_ext import build_ext as _build_ext
@@ -64,7 +70,7 @@ if_dl = lambda s: s if have_rtld else ''
 
 def get_abi3_suffix():
     """Return the file extension for an abi3-compliant Extension()"""
-    for suffix, _, _ in (s for s in imp.get_suffixes() if s[2] == imp.C_EXTENSION):
+    for suffix in EXTENSION_SUFFIXES:
         if '.abi3' in suffix:  # Unix
             return suffix
         elif suffix == '.pyd':  # Windows

setuptools/command/install_lib.py

 import os
-import imp
+import sys
 from itertools import product, starmap
 import distutils.command.install_lib as orig
 
@@ -74,10 +74,10 @@ class install_lib(orig.install_lib):
         yield '__init__.pyc'
         yield '__init__.pyo'
 
-        if not hasattr(imp, 'get_tag'):
+        if not hasattr(sys, 'implementation'):
             return
 
-        base = os.path.join('__pycache__', '__init__.' + imp.get_tag())
+        base = os.path.join('__pycache__', '__init__.' + sys.implementation.cache_tag)
         yield base + '.pyc'
         yield base + '.pyo'
         yield base + '.opt-1.pyc'