Fix FIXME in Builder::and and Builder::or impls

[fisherdarling]

Since a bug in gccjit was resolved: https://gcc.gnu.org/bugzilla//show_bug.cgi?id=95498 the Builder::and and Builder::or impl can be fixed and made much cleaner.

I think I did this right? Is there a list somewhere with the proper casting rules? I was a able to run ./test.sh and it made it through testing rust tests:
test result: FAILED. 4352 passed; 86 failed; 50 ignored; 0 measured; 0 filtered out; finished in 93.79s

closes #80

[antoyo]

Yup, you did it perfectly.

I was a bit surprised by your results locally, but the CI has 85 failures, so that's ok.

[fisherdarling]

Glad to hear that was right! I was a little confused if I had to do anything with int promotion (?) or something like that, but I guess not.

Also, is there a reason why rustfmt is not being used?

[antoyo]

I tried using rustfmt but couldn't get the formatting I wanted.

[antoyo]

Thanks for your work!
You had nothing to do with int promotion: there was actually a bug related to that in libgccjit and I fixed it.

[fisherdarling]

Thanks! I'll definitely pick up some other low-hanging fruit in the future.