Regression test: support big and little endian

Extracting a value from a union via a field of different size is
sensitive to endianness.

regression/cbmc-incr-smt2/unions/padded.desc

@@ -3,7 +3,7 @@ padded.c
 --trace
 Passing problem to incremental SMT2 solving
 \[main\.assertion\.1\] line 13 assertion my_union\.a \=\= 5\: FAILURE
-my_union\=\{ \.a\=\d+ \} \(\d{8} 00000101\)
+my_union\=\{ \.a\=\d+ \} \((\d{8} 00000101|00000101 \d{8})\)
 ^EXIT=10$
 ^SIGNAL=0$
 --