gh-85283: Fix _ctypes_test build on Windows in release mode

Define Py_BUILD_CORE to not attempt to link the extension to
python3.lib (which fails).

Author: vstinner

Modules/_ctypes/_ctypes_test.c

@@ -1,6 +1,11 @@
 // Need limited C API version 3.13 for Py_MOD_PER_INTERPRETER_GIL_SUPPORTED
 #define Py_LIMITED_API 0x030d0000
 
+// On Windows, Py_LIMITED_API requires Py_BUILD_CORE to not attempt linking the
+// stdlib extension to python3.lib (which fails). Then Python.h undefines
+// Py_BUILD_CORE when Py_LIMITED_API is defined.
+#define Py_BUILD_CORE
+
 #include <Python.h>
 
 #include <stdio.h>                // printf()