Improve ASCII Diffing for excluded tests

[Nikil-Shyamsunder]

In generate_runt_configs.py:

these cases are correct, but our ASCII diffing isn't good enough

# for us to know they are the same
xfailed = ["examples/serv/serv_regfile.tx",
           "tests/adders/adder_d1/wait_and_add_correct.tx",
           "tests/fifo/fifo.tx",
           "tests/fifo/push_pop_identity_ok.tx",
           "tests/wishbone/wishbone.tx"]