Quote 'setup.py install' when calling it legacy

We want to make it clear that it is the setup.py install command we consider
legacy, not setup.py itself.

Author: sbidoul

src/pip/_internal/commands/install.py

@@ -376,8 +376,8 @@ def run(self, options, args):
                 deprecated(
                     reason=(
                         "Could not build wheels for {} which do not use "
-                        "PEP 517. pip will fall back to legacy setup.py "
-                        "install for these.".format(
+                        "PEP 517. pip will fall back to legacy 'setup.py "
+                        "install' for these.".format(
                             ", ".join(r.name for r in legacy_build_failures)
                         )
                     ),

src/pip/_internal/wheel_builder.py

@@ -80,7 +80,7 @@ def _should_build(
     if not req.use_pep517 and not is_wheel_installed():
         # we don't build legacy requirements if wheel is not installed
         logger.info(
-            "Using legacy setup.py install for %s, "
+            "Using legacy 'setup.py install' for %s, "
             "since package 'wheel' is not installed.", req.name,
         )
         return False