Build ponyc-standalone.lib for windows

[mfelsche]

Build ponyc-standalone.lib for windows as a standalone variant of libponyc. It contains blake2, LLVM libs and libponyc.
It does not (to my knowledge) contain any static system libraries yet, but pony programs linked against it, work fine as is.

Linking to it from a pony program is done in the exact same way as for the other supported platforms:

use "lib:ponyc-standalone" if linux or osx or windows
use "lib:c++" if osx

actor Main
  new create(env: Env) =>
    None

[ponylang-main]

Hi @mfelsche,

The changelog - added label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 4307.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.

[SeanTAllen]

@mfelsche can you add release notes for this that mirror the final version of the MacOS release notes except for Windows? Then this should be good to merge.

[SeanTAllen]

is a libc++ not needed for windows? are we statically linking one?

[mfelsche]

Yes, those are always statically linked. I was testing this successfully on my Windows 10 machine.