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

Specifically, nlr.h does.
diff --git a/py/objzip.c b/py/objzip.c
index 4c7070b..c3bffd8 100644
--- a/py/objzip.c
+++ b/py/objzip.c
@@ -1,8 +1,8 @@
 #include <stdlib.h>
 #include <assert.h>
 
-#include "misc.h"
 #include "mpconfig.h"
+#include "misc.h"
 #include "qstr.h"
 #include "obj.h"
 #include "runtime.h"