gh-158810: Use _Py_TYPEOF in Py_ARRAY_LENGTH() (#158838)

Fix the compiler warning "extension used" when building test_cext
with clang.

* test_cext no longer overrides the CC environment variable if it's
  already defined.
* test_cext now also logs __STRICT_ANSI__ macro.

Author: vstinner

Include/pymacro.h

@@ -214,12 +214,12 @@
 //
 // gh-158810: Do not use __builtin_types_compatible_p() in strict C ANSI mode
 // and on C++.
-#if (defined(__GNUC__) && __GNUC__ >= 4 \
+#if (defined(__GNUC__) && __GNUC__ >= 4 && defined(_Py_TYPEOF) \
         && !defined(__STRICT_ANSI__) && !defined(__cplusplus))
 #define Py_ARRAY_LENGTH(array) \
     (sizeof(array) / sizeof((array)[0]) \
-     + Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(typeof(array), \
-                                                          typeof(&(array)[0]))))
+     + Py_BUILD_ASSERT_EXPR(!__builtin_types_compatible_p(_Py_TYPEOF(array), \
+                                                          _Py_TYPEOF(&(array)[0]))))
 #else
 #define Py_ARRAY_LENGTH(array) \
     (sizeof(array) / sizeof((array)[0]))

Lib/test/test_cext/extension.c

@@ -388,6 +388,11 @@ module_exec(PyObject *module)
         return -1;
     }
 #endif
+#ifdef __STRICT_ANSI__
+    if (PyModule_AddIntConstant(module, "__STRICT_ANSI__", 1) < 0) {
+        return -1;
+    }
+#endif
 #ifdef __cplusplus
     if (PyModule_AddIntMacro(module, __cplusplus) < 0) {
         return -1;

Lib/test/test_cext/runtests.py

@@ -28,7 +28,12 @@ def main():
     testmod = importlib.import_module(module_name)
 
     newline = False
-    for name in ('__STDC_VERSION__', '__cplusplus', '_MSVC_LANG'):
+    for name in (
+        '__STDC_VERSION__',
+        '__STRICT_ANSI__',
+        '__cplusplus',
+        '_MSVC_LANG',
+    ):
         try:
             value = getattr(testmod, name)
         except AttributeError:

Lib/test/test_cext/setup.py

@@ -135,7 +135,7 @@ def main():
     # option emits a C++ compiler warning. Remove "-std11" option from the
     # CC command.
     cmd = (sysconfig.get_config_var('CC') or '')
-    if cmd is not None:
+    if cmd is not None and 'CC' not in os.environ:
         if support.MS_WINDOWS:
             std_prefix = '/std'
         else: