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

Specifically, nlr.h does.
diff --git a/py/objfun.c b/py/objfun.c
index 7a1c3ff..e0c2577 100644
--- a/py/objfun.c
+++ b/py/objfun.c
@@ -7,9 +7,9 @@
 #include <malloc.h>
 #endif
 
+#include "mpconfig.h"
 #include "nlr.h"
 #include "misc.h"
-#include "mpconfig.h"
 #include "qstr.h"
 #include "obj.h"
 #include "objtuple.h"