bpo-38187: Fix reference leak in test_tools (GH-16233)

Lib/test/test_tools/test_c_analyzer/test_c_analyzer_common/test_known.py

@@ -15,6 +15,9 @@ class FromFileTests(unittest.TestCase):
 
     _return_read_tsv = ()
 
+    def tearDown(self):
+        Variable._isglobal.instances.clear()
+
     @property
     def calls(self):
         try:

Tools/c-analyzer/c_parser/info.py

@@ -22,6 +22,9 @@ class Variable(_NTBase,
     __slots__ = ()
     _isglobal = util.Slot()
 
+    def __del__(self):
+        del self._isglobal
+
     @classonly
     def from_parts(cls, filename, funcname, name, vartype, isglobal=False):
         id = info.ID(filename, funcname, name)