Address review

news/4799.bugfix

@@ -1 +0,0 @@
-Fix situation where build requirements are installed before calling setup.py.

src/pip/_internal/build_env.py

@@ -68,6 +68,9 @@ class BuildEnvironment(object):
 
 
 class NoOpBuildEnvironment(BuildEnvironment):
+    def __init__(self, no_clean):
+        pass
+
     def __enter__(self):
         pass
 

tests/data/src/pep518-3.0/setup.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python
 from setuptools import find_packages, setup
 
-import simple  # Test gh-4647 regression
+import simple  # ensure dependency is installed
 
 setup(name='pep518',
       version='3.0',