a94e72b5b7
This adds ISLE support for the s390x back-end and moves lowering of most instructions to ISLE. The only instructions still remaining are calls, returns, traps, and branches, most of which will need additional support in common code. Generated code is not intended to be (significantly) different than before; any additional optimizations now made easier to implement due to the ISLE layer can be added in follow-on patches. There were a few differences in some filetests, but those are all just simple register allocation changes (and all to the better!).
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.