Windows ARM64 Support

[mborland]

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.