do big-endian arrays with flatten_byte_extract

Author: Daniel Kroening

src/solvers/flattening/flatten_byte_operators.cpp

@@ -117,7 +117,10 @@ exprt flatten_byte_extract(
       for(mp_integer i=0; i<num_elements; ++i)
       {
         // the most significant byte comes first in the concatenation!
-        plus_exprt index(first_index, from_integer(num_elements-i-1, offset_type));
+        mp_integer index_offset=
+          little_endian?(num_elements-i-1):i;
+        
+        plus_exprt index(first_index, from_integer(index_offset, offset_type));
         concat.copy_to_operands(index_exprt(root, index));
       }