py, unix: Make "mpconfig.h" be first included, as other headers depend on it.

Specifically, nlr.h does.
diff --git a/py/objnamedtuple.c b/py/objnamedtuple.c
index 4239983..99a1d7b 100644
--- a/py/objnamedtuple.c
+++ b/py/objnamedtuple.c
@@ -1,7 +1,7 @@
 #include <string.h>
 
-#include "misc.h"
 #include "mpconfig.h"
+#include "misc.h"
 #include "nlr.h"
 #include "qstr.h"
 #include "obj.h"