Don’t try to install something when running from uninstalled source (#12246).
Original patch by Tshepang Lekhonkhobe.
diff --git a/Misc/NEWS b/Misc/NEWS
index 772eef9..e94b77c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -187,6 +187,10 @@
Library
-------
+- Issue #12246: Warn and fail when trying to install a third-party project from
+ an uninstalled Python (built in a source checkout). Original patch by
+ Tshepang Lekhonkhobe.
+
- Issue #11583: Speed up os.path.isdir on Windows by using GetFileAttributes
instead of os.stat.