fix generic endian detection for openbsd (aarch64 falls through to
the generic as we don't define __ARMEL__ or __ARMEB__).

Index: platform.h
--- platform.h.orig
+++ platform.h
@@ -141,11 +141,17 @@
 #if !IS_WINDOWS
 #include <sys/param.h>
 
-#if defined (__BYTE_ORDER)
+#if defined (__BYTE_ORDER__)
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define __FLASHROM_LITTLE_ENDIAN__ 1
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#define __FLASHROM_BIG_ENDIAN__ 1
+#endif
+#elif defined (__BYTE_ORDER)
 #if __BYTE_ORDER == __LITTLE_ENDIAN
-#define __FLASHROM_LITTLE_ENDIAN__
+#define __FLASHROM_LITTLE_ENDIAN__ 1
 #elif __BYTE_ORDER == __BIG_ENDIAN
-#define __FLASHROM_BIG_ENDIAN__
+#define __FLASHROM_BIG_ENDIAN__ 1
 #else
 #error Unknown byte order!
 #endif