gh-140210: Make test_sysconfig.test_parse_makefile_renamed_vars ignore environment variables (#140213)

The test did not expect it could be run with e.g. CFLAGS set to a custom value.

Lib/test/test_sysconfig.py

@@ -20,7 +20,7 @@
 )
 from test.support.import_helper import import_module
 from test.support.os_helper import (TESTFN, unlink, skip_unless_symlink,
-                                    change_cwd)
+                                    change_cwd, EnvironmentVarGuard)
 from test.support.venv import VirtualEnvironmentMixin
 
 import sysconfig
@@ -807,7 +807,9 @@ def test_parse_makefile_renamed_vars(self):
             print("PY_LDFLAGS=-lm", file=makefile)
             print("var2=$(LDFLAGS)", file=makefile)
             print("var3=$(CPPFLAGS)", file=makefile)
-        vars = _parse_makefile(TESTFN)
+        with EnvironmentVarGuard() as env:
+            env.clear()
+            vars = _parse_makefile(TESTFN)
         self.assertEqual(vars, {
             'var1': '-Wall',
             'CFLAGS': '-Wall',

Misc/NEWS.d/next/Tests/2025-10-16-15-08-58.gh-issue-140210.P9vUP8.rst

@@ -0,0 +1,2 @@
+Make ``test_sysconfig.test_parse_makefile_renamed_vars`` less fragile by
+clearing the environment variables before parsing the Makefile.