Don't allow both ENDIANNESSes to be set
See discussion on https://github.com/micropython/micropython/commit/2da81fa80c4cd965f05ad237d81d9764322fde20
Explicitly set `MP_ENDIANNESS_LITTLE` because that's the #define that is used in code elsewhere.
diff --git a/py/mpconfig.h b/py/mpconfig.h
index f9c02a6..a0b6e9d 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -187,6 +187,10 @@
// Just because most archs are such?
#define MP_ENDIANNESS_LITTLE (1)
#endif
+// Ensure we don't accidentally set both endiannesses
+#if MP_ENDIANNESS_BIG
+#define MP_ENDIANNESS_LITTLE (0)
+#endif
// printf format spec to use for machine_int_t and friends
#ifndef INT_FMT