bpo-26789: Fix logging.FileHandler._open() at exit (GH-23053)

The logging.FileHandler class now keeps a reference to the builtin
open() function to be able to open or reopen the file during Python
finalization.

Fix errors like:

    Exception ignored in: (...)
    Traceback (most recent call last):
      (...)
      File ".../logging/__init__.py", line 1463, in error
      File ".../logging/__init__.py", line 1577, in _log
      File ".../logging/__init__.py", line 1587, in handle
      File ".../logging/__init__.py", line 1649, in callHandlers
      File ".../logging/__init__.py", line 948, in handle
      File ".../logging/__init__.py", line 1182, in emit
      File ".../logging/__init__.py", line 1171, in _open
    NameError: name 'open' is not defined

1 files changed, 1 insertions, 1 deletions

diff --git a/Python/_warnings.c b/Python/_warnings.c
index 271cd47..3c048af 100644
--- a/Python/_warnings.c
+++ b/Python/_warnings.c
@@ -852,7 +852,7 @@ setup_context(Py_ssize_t stack_level, PyObject **filename, int *lineno,
     }
 
     if (f == NULL) {
-        globals = _PyInterpreterState_GET()->sysdict;
+        globals = tstate->interp->sysdict;
         *filename = PyUnicode_FromString("sys");
         *lineno = 1;
     }