Do not attempt setup.py clean for failed pep517 builds

Fixes pypa#6642

Author: sbidoul

news/6642.bugfix

@@ -0,0 +1,2 @@
+Do not attempt to run ``setup.py clean`` after a ``pep517`` build error,
+since a ``setup.py`` may not exist in that case.

src/pip/_internal/wheel_builder.py

@@ -349,10 +349,11 @@ def _build_one_inside_env(
                 except Exception:
                     pass
             # Ignore return, we can't do anything else useful.
-            self._clean_one(req)
+            if not req.use_pep517:
+                self._clean_one_legacy(req)
             return None
 
-    def _clean_one(self, req):
+    def _clean_one_legacy(self, req):
         # type: (InstallRequirement) -> bool
         clean_args = make_setuptools_clean_args(
             req.setup_py_path,