Fix detection of big-endian systems.
https://sourceforge.net/p/resil/tickets/8/
https://github.com/DentonW/DevIL/pull/85
--- src-IL/include/il_endian.h.orig	2017-01-01 18:03:56.000000000 -0600
+++ src-IL/include/il_endian.h	2020-07-05 09:02:34.000000000 -0500
@@ -25,7 +25,7 @@
 #endif
 #endif
 
-#if (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __BIG_ENDIAN__) \
+#if (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__) \
   || (defined(__BIG_ENDIAN__) && !defined(__LITTLE_ENDIAN__))
 #undef __LITTLE_ENDIAN__
 #define Short(s) iSwapShort(s)