Use the proper autoconf macro for checking byte order.
The BYTEORDER_IS_BIG_ENDIAN macro is defined Objects/unicodeobject.c,
thus the code was always emitting the little-endian machine format codes.
This should fix the failure seen on the SPARC buildbot.
diff --git a/Modules/arraymodule.c b/Modules/arraymodule.c
index 236c952..0ac3cab 100644
--- a/Modules/arraymodule.c
+++ b/Modules/arraymodule.c
@@ -1526,7 +1526,7 @@
static enum machine_format_code
typecode_to_mformat_code(int typecode)
{
-#ifdef BYTEORDER_IS_BIG_ENDIAN
+#ifdef WORDS_BIGENDIAN
const int is_big_endian = 1;
#else
const int is_big_endian = 0;