### Checklist
- [X] I've run tests to see all new and existing tests pass
- [X] I've followed the code style of the rest of the project
- [X] I've read the [Contribution Guidelines](CONTRIBUTING.md)
- [X] I've updated the documentation if necessary

#### If you've made changes to `gyb` files
- [X] I've run `.script/generate_boilerplate_files_with_gyb` and
included updated generated files in a commit of this pull request

### Motivation:

When building SwiftPM with CMake and the swift-crypto package there are
errors being produced on macOS relating to missing imports provided by
the CryptoKit package.

### Modifications:

Modify the CMakeLists.txt file for the Crypto target so that the defines
are set like they are in the Package.swift.

### Result:

After the change, building SwiftPM with CMake on macOS should work.

Remove the extra true values for the swift defines in the CryptoExtras
modules CMakeLists.txt file.

### Checklist
- [X] I've run tests to see all new and existing tests pass
- [X] I've followed the code style of the rest of the project
- [X] I've read the [Contribution Guidelines](CONTRIBUTING.md)
- [X] I've updated the documentation if necessary

#### If you've made changes to `gyb` files
- [X] I've run `.script/generate_boilerplate_files_with_gyb` and
included updated generated files in a commit of this pull request

### Motivation:

The defines don't take effect with a value. Remove the value "true" from
them.

### Modifications:

Modified the CMakeLists.txt file in the CryptoExtras module.

### Result:

After the change the swift defines will hopefully be defined correctly.

…g/ASM (#325)

When building using CMake with Windows, there is an error regarding
missing MultithreadedDLL support. Work around this by setting the
MSVC_RUNTIME_LIBRARY on that platform to a supported option.

### Checklist
- [X] I've run tests to see all new and existing tests pass
- [X] I've followed the code style of the rest of the project
- [X] I've read the [Contribution Guidelines](CONTRIBUTING.md)
- [X] I've updated the documentation if necessary

#### If you've made changes to `gyb` files
- [X] I've run `.script/generate_boilerplate_files_with_gyb` and
included updated generated files in a commit of this pull request

### Motivation:

I'm trying to build swift-crypto on Windows with CMake.

### Modifications:

I've modified the CMakelists.txt such that the clang can compile the
assembly files on Windows.

### Result:

Hopefully, Windows builds of swift-crypto are working.

)

## Motivation

We would like to provide support for ARCV1(P-384), as defined in [IETF
Internet Draft: Anonymous Rate-Limited
Credentials](https://datatracker.ietf.org/doc/draft-yun-cfrg-arc/).

## Modifications

- Add internal implementation, generic over the NIST curves.
- Add public API for ARC(P-384), under `P384._ARCV1`.

## Result

New API for current draft of ARC.

## Tests

- End to end tests of internal implementation and API surface.
- Test vector tests of internal implementation and API surface, from the
spec draft.

This change prepares swift-crypto for use on Windows with CMake and also
the Package.swift for use in the Swift toolchain CI system.

### Checklist
- [X] I've run tests to see all new and existing tests pass
- [X] I've followed the code style of the rest of the project
- [X] I've read the [Contribution Guidelines](CONTRIBUTING.md)
- [X] I've updated the documentation if necessary

#### If you've made changes to `gyb` files
- [X] I've run `.script/generate_boilerplate_files_with_gyb` and
included updated generated files in a commit of this pull request

### Motivation:

Upgrading swift-crypto from an older version requires that Windows works
properly with CMake, and also SwiftPM.

### Modifications:

Modify the CMakeLists.txt files and the generator script so that it
conditionally adds assembly files for non-Windows platforms. Prepare the
Package.swift file for use in Swift CI pipelines, by consulting an
environment to either use the absolute URL, or a prepared version of the
swift-asn1 dependency.

### Result:

After this change it should be possible to build with the newest
swift-crypto in the Swift CI system.