Implement ARM64 [was: arm64: test "double_finalize" failed with panic 'not yet implemented']

System is an Ampere eMag, Packet c2.large.arm.

Build succeeds after applying the patch in bytecodealliance/cranelift#716 but a few tests fail.

```
test double_finalize ... FAILED
```

```
thread 'double_finalize' panicked at 'not yet implemented', cranelift-codegen/sr
c/isa/arm64/abi.rs:15:5
```