Add --enable-languages=all,ada,go

Also, update the comment in compare-builds.sh listing the expected .sum
files: we've lost:

  build/x86_64-unknown-linux-gnu/libmudflap/testsuite/libmudflap.sum

due to Mudflap's upstream removal in 4.9, and gained:

  build/gcc/testsuite/ada/acats/acats.sum
  build/gcc/testsuite/gnat/gnat.sum
  build/gcc/testsuite/go/go.sum
  build/x86_64-unknown-linux-gnu/libgo/libgo.sum

due to the --enable-languages=all,ada,go