Windows ARM64 Support

Two probably related issues with using Windows on ARM64 using Parallels:

1) When using B2 the output of configuration checks is:

```
- default address-model : 64-bit [1]
- default architecture : none [1]
```

If you specify `architecture=arm` on the command line things build and run just fine

2) When using CMAKE the configuration step successfully completes, but the build always fails with: `unknown command-line argument or argument value -DBOOST_CONTEXT_EXPORT=`

I am able to build and run CMAKE using the x64 cross compiler after manually specifying the architecture and the assembler in Visual Studio.