- Issue #11171: Fix detection of config/Makefile when --prefix !=

  --exec-prefix, which caused Python to not start.

Lib/sysconfig.py

@@ -271,7 +271,7 @@ def _parse_makefile(filename, vars=None):
 def _get_makefile_filename():
     if _PYTHON_BUILD:
         return os.path.join(_PROJECT_BASE, "Makefile")
-    return os.path.join(get_path('stdlib'), "config", "Makefile")
+    return os.path.join(get_path('platstdlib'), "config", "Makefile")
 
 
 def _init_posix(vars):

Misc/NEWS

@@ -37,6 +37,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #11171: Fix detection of config/Makefile when --prefix !=
+  --exec-prefix, which caused Python to not start.
+
 - Issue #11116: any error during addition of a message to a mailbox now causes
   a rollback, instead of leaving the mailbox partially modified.