Issue #21923: merge from 3.4

diff --cc Misc/NEWS
index 0d32cf3ca859e51483f51f69fd87fe7f78048e16,97ffbfc01aa01567995f122e44bf02eccb4780d4..edd46d86cb05ad2e9eacbcb4a7d7b2cd9e64c4ad
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -539,15 -467,10 +539,17 @@@ Librar
  - Issue #11571: Ensure that the turtle window becomes the topmost window
    when launched on OS X.
  
 -Extension Modules
 ------------------
 +- Issue #21801: Validate that __signature__ is None or an instance of Signature.
  
 -- Issue #21276: posixmodule: Don't define USE_XATTRS on KFreeBSD and the Hurd.
++- Issue #21923: Prevent AttributeError in distutils.sysconfig.customize_compiler
++  due to possible uninitialized _config_vars.
 +
 +Extension Modules
 +-----------------
 +
 +- Issue #21407: _decimal: The module now supports function signatures.
 +
 +- Issue #21276: posixmodule: Don't define USE_XATTRS on KFreeBSD and the Hurd.
  - Issue #21226: Set up modules properly in PyImport_ExecCodeModuleObject
    (and friends).