Warn when assigning to __debug__ instead of raising an error.
diff --git a/Python/compile.c b/Python/compile.c
index df514c7..1fb85e7 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -5185,13 +5185,8 @@
 			n = CHILD(n, 1);
 			goto loop;
 		} else if (TYPE(tmp) == NAME) {
-			if (strcmp(STR(tmp), "__debug__") == 0) {
-				PyErr_SetString(PyExc_SyntaxError,
-						ASSIGN_DEBUG);
- 				PyErr_SyntaxLocation(st->st_filename,
-						   n->n_lineno);
-				st->st_errors++;
-			}
+			if (strcmp(STR(tmp), "__debug__") == 0)
+				symtable_warn(st, ASSIGN_DEBUG);
 			symtable_add_def(st, STR(tmp), DEF_LOCAL | flag);
 		}
 		return;