[3.7] bpo-9263: _PyObject_Dump() detects freed memory (GH-10061) (GH-10662)

* bpo-9263: _PyObject_Dump() detects freed memory (GH-10061)

_PyObject_Dump() now uses an heuristic to check if the object memory
has been freed: log "<freed object>" in that case.

The heuristic rely on the debug hooks on Python memory allocators
which fills the memory with DEADBYTE (0xDB) when memory is
deallocated. Use PYTHONMALLOC=debug to always enable these debug
hooks.

(cherry picked from commit 82af0b63b07aa8d92b50098e382b458143cfc677)

* bpo-9263: Fix _PyObject_Dump() for freed object (#10661)

If _PyObject_Dump() detects that the object is freed, don't try to
dump it (exit immediately).

Enhance also _PyObject_IsFreed(): it now detects if the pointer
itself looks like freed memory.

(cherry picked from commit 2cf5d32fd9e61488e8b0be55a2e92a752ba8b06b)
diff --git a/Include/pymem.h b/Include/pymem.h
index 8ee0efd..ef6e0bb 100644
--- a/Include/pymem.h
+++ b/Include/pymem.h
@@ -55,7 +55,9 @@
 PyAPI_FUNC(PyObject*) _PyTraceMalloc_GetTraceback(
     unsigned int domain,
     uintptr_t ptr);
-#endif   /* !Py_LIMITED_API */
+
+PyAPI_FUNC(int) _PyMem_IsFreed(void *ptr, size_t size);
+#endif   /* !defined(Py_LIMITED_API) */
 
 
 /* BEWARE: