aarch64 fails with newer glibc (ipc_perm.mode)

[posborne]

I'm playing around with some changes that make it easier to run the tests for multiple architectures locally based on recent work merged into Nix. Running the build/tests in posborne/rust-cross:arm which is based on Ubuntu 15.10, this following error is received:

/data/aarch64-unknown-linux-gnu/debug/build/libc-test-2ff1f50e28187d2d/out/all.c: In function '__test_field_type_ipc_perm_mode':
/data/aarch64-unknown-linux-gnu/debug/build/libc-test-2ff1f50e28187d2d/out/all.c:9148:21: error: return from incompatible pointer type [-Werror]
                     return &b->mode;
                     ^
cc1: all warnings being treated as errors
thread '<main>' panicked at 'explicit panic', /root/.multirust/toolchains/1.7.0/cargo/registry/src/github.com-88ac128001ac3a9a/gcc-0.3.25/src/lib.rs:818

It appears that the type of struct ipc_perm.mode has a differnt type (mode_t I think). Not sure how best to handle. Simply changing the type to mode_t causes other failures.

[alexcrichton]

How did glibc change in this regard? If it wasn't just switching to mode_t, did other pieces change as well?

[kamalmarhubi]

Aside: @posborne I'm really excited for your testing changes here!