gh-128978: Fix a NameError in sysconfig.expand_makefile_vars (#128979)

This fixes a regression introduced by 4a53a397c3.

Lib/sysconfig/__init__.py

@@ -718,6 +718,9 @@ def expand_makefile_vars(s, vars):
     """
     import re
 
+    _findvar1_rx = r"\$\(([A-Za-z][A-Za-z0-9_]*)\)"
+    _findvar2_rx = r"\${([A-Za-z][A-Za-z0-9_]*)}"
+
     # This algorithm does multiple expansion, so if vars['foo'] contains
     # "${bar}", it will expand ${foo} to ${bar}, and then expand
     # ${bar}... and so forth.  This is fine as long as 'vars' comes from

Misc/NEWS.d/next/Library/2025-01-18-11-04-44.gh-issue-128978.hwg7-w.rst

@@ -0,0 +1,2 @@
+Fix a :exc:`NameError` in :func:`!sysconfig.expand_makefile_vars`. Patch by
+Bénédikt Tran.