Implement prefetch data intrinsics

[NCGThompson]

Fixes #414

It should probably have tests that should fail before the changes. What kind of test should I add?

I edited the builtin list in context.rs, and that might create a conflict when syncing with the rust repository.

[antoyo]

It should probably have tests that should fail before the changes. What kind of test should I add?

Do you know what kind of tests there is for this in the LLVM codegen?

[NCGThompson]

The codegen tests are probably the most thorough, but they are LLVM specific. However, according to the FileCheck documentation, it doesn't do much that can't be done with grep.

At a minimum though, I think we should check that the compiler can encounter the function without panicking.

[antoyo]

At a minimum though, I think we should check that the compiler can encounter the function without panicking.

I would be OK with such a test. You can add it in this directory.

[antoyo]

Is this still a draft or should I review this PR?

[antoyo]

Oh, sorry, I didn't notice you marked this PR as ready for review (please ping me if I don't answer for some time: I can easily miss some things).

There are some conflicts to fix.