* Add support for processor features (including auto-detection).
* Move base architecture set requirement back to z14.
* Add z15 feature sets and re-enable z15-specific code generation
when required features are available.
cranelift-codegen's build failed on s390x, with this error:
```
error[E0432]: unresolved import `crate::isa::unwind::systemv`
--> cranelift/codegen/src/isa/s390x/mod.rs:6:25
|
6 | use crate::isa::unwind::systemv::RegisterMappingError;
| ^^^^^^^ could not find `systemv` in `unwind`
```
This import should be used only with `unwind` feature enabled.
This is sometimes useful when performing analyses on the generated
machine code: for example, some kinds of code verifiers will want to do
a control-flow analysis, and it is much easier to do this if one does
not have to recover the CFG from the machine code (doing so requires
heavyweight analysis when indirect branches are involved). If one trusts
the control-flow lowering and only needs to verify other properties of
the code, this can be very useful.
This adds support for the IBM z/Architecture (s390x-ibm-linux).
The status of the s390x backend in its current form is:
- Wasmtime is fully functional and passes all tests on s390x.
- All back-end features supported, with the exception of SIMD.
- There is still a lot of potential for performance improvements.
- Currently the only supported processor type is z15.
