[3.13] gh-128978: Fix a `NameError` in `sysconfig.expand_makefile_vars` (GH-128979) (#129065)

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

This fixes a regression introduced by 4a53a397c311567f05553bc25a28aebaba4f6f65.
(cherry picked from commit df66ff14b49f4388625212f6bc86b754cb51d4eb)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>