Antimony: exploring alternative build systems

[wes1 (Wes)]

@compnerd

@kateinoigakukun worked on a GSoC project to enable LTO which ran into some (non-technical) issues that prevented the work from being fully realized.

For reference

• https://github.com/kateinoigakukun/swift-lto-benchmark
• [GSoC] LTO support progress report (with some design discussion and status)