build: comparison tool swap

This should be functionally identical to what's in place now. It was built from
https://github.com/theuni/bitcoinj/commit/be0eef774462409df277b2a83d71c30451f107c5

That commit is the same as this pruned commit in TheBlueMatt's repo:
https://github.com/TheBlueMatt/bitcoinj/commit/0f7b5d8

Now we'll be able to trust the line numbers in the stack traces.