[2.7] bpo-31675: Fix memory leaks in Tkinter's methods splitlist() and split() (GH-3866) (#3876)

when pass a string larger than 2 GiB.

Decrease memory requirements for Tcl's bigmem tests..
(cherry picked from commit 27c623c845dd6e4b8e1782666ca3a956636da266)
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index 6053e4b..444c268 100644
--- a/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@ -2332,7 +2332,11 @@
     if (!PyArg_ParseTuple(args, "et:splitlist", "utf-8", &list))
         return NULL;
 
-    CHECK_STRING_LENGTH(list);
+    if (strlen(list) >= INT_MAX) {
+        PyErr_SetString(PyExc_OverflowError, "string is too long");
+        PyMem_Free(list);
+        return NULL;
+    }
     if (Tcl_SplitList(Tkapp_Interp(self), list,
                       &argc, &argv) == TCL_ERROR)  {
         PyMem_Free(list);
@@ -2394,7 +2398,11 @@
 
     if (!PyArg_ParseTuple(args, "et:split", "utf-8", &list))
         return NULL;
-    CHECK_STRING_LENGTH(list);
+    if (strlen(list) >= INT_MAX) {
+        PyErr_SetString(PyExc_OverflowError, "string is too long");
+        PyMem_Free(list);
+        return NULL;
+    }
     v = Split(list);
     PyMem_Free(list);
     return v;