Get endianness into Makefile variable

Makefile.system

@@ -1328,6 +1328,7 @@ export OSNAME
 export ARCH
 export CORE
 export LIBCORE
+export __BYTE_ORDER__
 export PGCPATH
 export CONFIG
 export CC

getarch.c

@@ -1298,6 +1298,13 @@ int main(int argc, char *argv[]){
 #endif
 #endif
 
+#if defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+printf("__BYTE_ORDER__=__ORDER_BIG_ENDIAN__\n");
+#endif
+#if defined(__BIG_ENDIAN__) && __BIG_ENDIAN__ > 0
+printf("__BYTE_ORDER__=__ORDER_BIG_ENDIAN__\n");
+#endif
+
 #ifdef MAKE_NB_JOBS
   #if MAKE_NB_JOBS > 0
     printf("MAKE += -j %d\n", MAKE_NB_JOBS);