Merge branch 'aarch64' into 'redox'

.gitmodules

src/librustc_target/spec/aarch64_unknown_redox.rs

src/librustc_target/spec/mod.rs

src/librustc_target/spec/redox_base.rs

src/libstd/sys/redox/syscall/arch/aarch64.rs

src/libstd/sys/redox/syscall/mod.rs

src/llvm

src/tools/build-manifest/src/main.rs