Source builds for openssl, libcurl, and libxml

For the official Android SDK (to be eventually tracked at https://github.com/orgs/swiftlang/projects/17), we will need to replace the [Termux binaries](https://github.com/finagolfin/swift-android-sdk/blob/8ccdf2935fcfa07a08acc21b47a91f8366325bbd/get-packages-and-swift-source.swift#L7C163-L7C170) with source builds for the dependencies of FoundationXML (libxml) and FoundationNetworking (curl and openssl). The [Readdle SDK action](https://github.com/readdle/swift-android-toolchain/actions) is already doing this: https://github.com/readdle/swift-android-toolchain/blob/release/6.1/build/043-build-libxml.sh https://github.com/readdle/swift-android-toolchain/blob/release/6.1/build/042-build-curl.sh https://github.com/readdle/swift-android-toolchain/blob/release/6.1/build/041-build-openssl.sh I recommend we rework these scripts to integrate them into [sdks.yml](https://github.com/finagolfin/swift-android-sdk/blob/main/.github/workflows/sdks.yml). If amenable, I can work on a PR for this.