musl: use of undeclared type name libc::ucontext_t

[posborne]

x86_64-unknown-linux-musl should be added to CI. It is included in the posborne/rust-cross:x86 docker image. Discovered this while working on some fixup for the CI stuff. May be a libc issue.

=======================================================
TESTING VERSION: 1.7.0, TARGET: x86_64-unknown-linux-musl
=======================================================
/source/src/ucontext.rs:7:14: 7:30 error: use of undeclared type name `libc::ucontext_t` [E0412]
/source/src/ucontext.rs:7     context: libc::ucontext_t,
                                       ^~~~~~~~~~~~~~~~
/source/src/ucontext.rs:7:14: 7:30 help: run `rustc --explain E0412` to see a detailed explanation

[posborne]

@kamalmarhubi Can you please label this as appropriate. I don't seem to have the ability to create new labels.

[kamalmarhubi]

@posborne I think you should be able to do this now. I created a "team" and gave it admin access on the repo. Added some labels though!

[posborne]

I started looking at things a bit -- there are some legit test problems in ioctl and a few other places. I started looking more at using ctest to do the types of checks we are doing in some places (some of this need goes away with moving contants to libc, but some will likely need to remain).

I ended up bumping into rust-lang/cargo#1430 and decided to take a break.

[fiveop]

I made a patch for libc, that adds ucontext for linux-musl ( rust-lang/libc#255 ). That should resolve this.

[fiveop]

musl does not implement the functions working on ucontext structs (http://wiki.musl-libc.org/wiki/Open_Issues#ucontext.h), so let's see how far the struct gets us.