Merge pull request #1 from dlrobertson/aarch64_valist

deps/helper/Cargo.toml

deps/helper/build.rs

src/impl-aarch64-elf.rs

src/impl-arm-sysv.rs

src/impl-x86-sysv.rs

src/impl-x86_64-elf.rs

src/impl-x86_64-win64.rs

src/lib.rs

tests/lib.rs