Support for Windows on Arm

When calling emsdk.bat with an arm64 python, it fails with following error:

```
$ file $(which python)
/c/wenv/arm64/python/tools/python: PE32+ executable (console) Aarch64, for MS Windows
$ cmd.exe /c 'emsdk.bat install latest'
Resolving SDK alias 'latest' to '3.1.23'
Resolving SDK version '3.1.23' to 'sdk-releases-upstream-bfd5e63a44ba4c8568cd8ac87c27b35e40732bf4-64bit'
error: tool or SDK not found: 'sdk-releases-upstream-bfd5e63a44ba4c8568cd8ac87c27b35e40732bf4-64bit'
```

Since this platform is not yet supported, this workaround (https://github.com/emscripten-core/emsdk/pull/1115) could be used.

Beyond that, it would be nice to offer a native toolchain for this new platform.