[3.9] bpo-40826: Fix GIL usage in PyOS_Readline() (GH-20613) (GH-20616)

* bpo-40826: Fix GIL usage in PyOS_Readline() (GH-20579)

Fix GIL usage in PyOS_Readline(): lock the GIL to set an exception.

Pass tstate to my_fgets() and _PyOS_WindowsConsoleReadline(). Cleanup
these functions.

(cherry picked from commit c353764fd564e401cf47a5d9efab18c72c60014e)

* bpo-40826: Add _PyOS_InterruptOccurred(tstate) function (GH-20599)

my_fgets() now calls _PyOS_InterruptOccurred(tstate) to check for
pending signals, rather calling PyOS_InterruptOccurred().

my_fgets() is called with the GIL released, whereas
PyOS_InterruptOccurred() must be called with the GIL held.

test_repl: use text=True and avoid SuppressCrashReport in
test_multiline_string_parsing().

Fix my_fgets() on Windows: fgets(fp) does crash if fileno(fp) is closed.

(cherry picked from commit fa7ab6aa0f9a4f695e5525db5a113cd21fa93787)
diff --git a/Modules/signalmodule.c b/Modules/signalmodule.c
index 0c9a267..119fc35 100644
--- a/Modules/signalmodule.c
+++ b/Modules/signalmodule.c
@@ -187,14 +187,20 @@
 #endif
 
 static int
-is_main(_PyRuntimeState *runtime)
+is_main_interp(_PyRuntimeState *runtime, PyInterpreterState *interp)
 {
     unsigned long thread = PyThread_get_thread_ident();
-    PyInterpreterState *interp = _PyRuntimeState_GetThreadState(runtime)->interp;
     return (thread == runtime->main_thread
             && interp == runtime->interpreters.main);
 }
 
+static int
+is_main(_PyRuntimeState *runtime)
+{
+    PyInterpreterState *interp = _PyRuntimeState_GetThreadState(runtime)->interp;
+    return is_main_interp(runtime, interp);
+}
+
 static PyObject *
 signal_default_int_handler(PyObject *self, PyObject *args)
 {
@@ -1726,12 +1732,14 @@
     finisignal();
 }
 
+
+// The caller doesn't have to hold the GIL
 int
-PyOS_InterruptOccurred(void)
+_PyOS_InterruptOccurred(PyThreadState *tstate)
 {
     if (_Py_atomic_load_relaxed(&Handlers[SIGINT].tripped)) {
         _PyRuntimeState *runtime = &_PyRuntime;
-        if (!is_main(runtime)) {
+        if (!is_main_interp(runtime, tstate->interp)) {
             return 0;
         }
         _Py_atomic_store_relaxed(&Handlers[SIGINT].tripped, 0);
@@ -1740,6 +1748,16 @@
     return 0;
 }
 
+
+// The caller must to hold the GIL
+int
+PyOS_InterruptOccurred(void)
+{
+    PyThreadState *tstate = _PyThreadState_GET();
+    return _PyOS_InterruptOccurred(tstate);
+}
+
+
 static void
 _clear_pending_signals(void)
 {