Backport copying recursion limit from C to test.support

Partially backport Python 3.13 changes that expose the C recursion
limit as _testcapi.Py_C_RECURSION_LIMIT and use them in test.support
rather than (incompletely) duplicating the values from header.  This
should fix test failures on platforms that were not correctly covered
in the Python code (e.g. SPARC).

The code is roughly based on parts of the following upstream commits:

45e09f9 pythonGH-112215: Increase C recursion limit for non debug builds (pythonGH-113397)
7e135a4 pythongh-111520: Integrate the Tier 2 interpreter in the Tier 1 interpreter (python#111428)
b0edf3b pythonGH-91079: Rename C_RECURSION_LIMIT to Py_C_RECURSION_LIMIT (python#108507)

Lib/test/support/__init__.py

@@ -2375,8 +2375,17 @@ def adjust_int_max_str_digits(max_digits):
     finally:
         sys.set_int_max_str_digits(current)
 
+def _get_c_recursion_limit():
+    try:
+        import _testcapi
+        return _testcapi.Py_C_RECURSION_LIMIT
+    except ImportError:
+        return 8000
+
+C_RECURSION_LIMIT = _get_c_recursion_limit()
+
 #For recursion tests, easily exceeds default recursion limit
-EXCEEDS_RECURSION_LIMIT = 5000
+EXCEEDS_RECURSION_LIMIT = C_RECURSION_LIMIT * 3
 
 # The default C recursion limit (from Include/cpython/pystate.h).
 if Py_DEBUG:

Modules/_testcapimodule.c

@@ -3954,6 +3954,8 @@ PyInit__testcapi(void)
     PyModule_AddObject(m, "instancemethod", (PyObject *)&PyInstanceMethod_Type);
 
     PyModule_AddIntConstant(m, "the_number_three", 3);
+#define Py_C_RECURSION_LIMIT C_RECURSION_LIMIT
+    PyModule_AddIntMacro(m, Py_C_RECURSION_LIMIT);
 
     if (PyModule_AddIntMacro(m, Py_single_input)) {
         return NULL;