SSA backend that performs ABI lowering and emits native amd64 ELF binaries

The aowl lowering pass: .s.aif to .c.aif (ARC, closures, exceptions, monomorphisation, dce, inlining), vendoring Araq's 25 nimony/hexer passes so the toolchain owns its own lowering.

Intermediate representation and lowering from the AST.