Auto merge of #824 - malbarbo:x32-1, r=alexcrichton

Fixes and test for x86_64-unknown-linux-gnux32

This fixes all libc tests and almost all rustc tests (3 libstd tests and one run-pass test fails).

Fixes https://github.com/rust-lang/libc/issues/816https://github.com/rust-lang/libc/issues/816