Fix test failure on Python 3.12 (fixes osandov#298)

Running tests on Python 3.12, we get:

test_int (tests.test_language_c.TestLiteral.test_int) ... python3.12: /usr/include/python3.12/object.h:215: Py_SIZE: Assertion `ob->ob_type != &PyLong_Type' failed.
Aborted (core dumped)

We're relying on an implementation detail to check whether the object is
negative. Instead, catch an overflow error, negate and try again.
Genuine overflows will still overflow on the second time, but negative
numbers will succeed.

Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>

libdrgn/python/object.c

@@ -18,15 +18,20 @@ static int DrgnObject_literal(struct drgn_object *res, PyObject *literal)
 	if (PyBool_Check(literal)) {
 		err = drgn_object_bool_literal(res, literal == Py_True);
 	} else if (PyLong_Check(literal)) {
-		bool is_negative = Py_SIZE(literal) < 0;
-		if (is_negative) {
+		bool is_negative = false;
+		uint64_t uvalue = PyLong_AsUint64(literal);
+
+		/* Assume an overflow is due to a negative number and retry */
+		if (uvalue == (uint64_t)-1 && PyErr_Occurred() &&
+		    PyErr_ExceptionMatches(PyExc_OverflowError)) {
+			is_negative = true;
+			PyErr_Clear();
 			literal = PyNumber_Negative(literal);
 			if (!literal)
 				return -1;
-		}
-		uint64_t uvalue = PyLong_AsUint64(literal);
-		if (is_negative)
+			uvalue = PyLong_AsUint64(literal);
 			Py_DECREF(literal);
+		}
 		if (uvalue == (uint64_t)-1 && PyErr_Occurred())
 			return -1;
 		err = drgn_object_integer_literal(res, uvalue);