[aws] Support building AWS packages on ARM Linux

[csw]

This adds support for building the AWS packages on Linux on ARM. (Tested with the arm64-linux triplet.) In particular, this allows using them in native Docker containers on Macs with Apple Silicon. These ports previously had the platform constraint !arm & !uwp, presumably because they wouldn't build on Windows on ARM, but this prevented them from being built on Linux on ARM as well. This is only a change to those platform constraints; the packages build successfully, and the subset that I've tested work normally.

• What does your PR fix?

  Fixes incompatibility with Linux on ARM.

• Which triplets are supported/not supported? Have you updated the CI baseline?

  No changes to supported triplets, adds support for arm-linux and arm64-linux. These are not part of CI, so I haven't changed the CI baseline.

• Does your PR follow the maintainer guide?

  Yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

  Yes

[github-actions]

You have modified or added at least one vcpkg.json where a "license" field is missing.

If you feel able to do so, please consider adding a "license" field to the following files:

• ports/aws-c-auth/vcpkg.json
• ports/aws-c-cal/vcpkg.json
• ports/aws-c-common/vcpkg.json
• ports/aws-c-compression/vcpkg.json
• ports/aws-c-event-stream/vcpkg.json
• ports/aws-c-http/vcpkg.json
• ports/aws-c-io/vcpkg.json
• ports/aws-c-mqtt/vcpkg.json
• ports/aws-c-s3/vcpkg.json
• ports/aws-checksums/vcpkg.json
• ports/aws-crt-cpp/vcpkg.json
• ports/aws-sdk-cpp/vcpkg.json

Valid values for the license field can be found in the documentation