bpo-35224: Reverse evaluation order of key: value in dict comprehensions (GH-14139)

… as proposed in PEP 572; key is now evaluated before value.

https://bugs.python.org/issue35224
(cherry picked from commit c8a35417db)

Co-authored-by: Jörn Heissler <joernheissler@users.noreply.github.com>

Python/ceval.c

@@ -2944,8 +2944,8 @@ main_loop:
         }
 
         case TARGET(MAP_ADD): {
-            PyObject *key = TOP();
-            PyObject *value = SECOND();
+            PyObject *value = TOP();
+            PyObject *key = SECOND();
             PyObject *map;
             int err;
             STACK_SHRINK(2);