Looks like ubuntu 17.04 is broken now and it fails to link on 17.10 and 18.04.
It seems to work on stretch though!

Apparently 17.04 is broken now?

Looks like `cargo test` is now trying to test too many files due to
rust-lang/cargo#4750 so add a clause to the wrapper to ignore the bogus ones for
now

It wasn't expecting a `*.d` file to exist, now it does.

Pure sh scripts should use /bin/sh as it's available on every platform.

When using bash-specific features, use env to find it, as bash can
be installed in different places according the OS.

* Add syscall tables to most remaining arches in `src/unix/notbsd`
* Add aarch64/arm musl to CI
* Update dependencies

Apparently it no longer works

Signed-off-by: Tom Kirchner <tjk@amazon.com>
Signed-off-by: Ben Cressey <bcressey@amazon.com>

Apparently the 17.10 image broke?

Rebase of #610 and also move emscripten up much higher in the hierarchy to
ensure that it doesn't have too much of a ripple effect on other platforms.

This involved moving down a good number of definitions, but hopefully was done
with care to not break anything!

This works by specifying a "runner" for actually executing the binary.
This doesn't apply to the Android or NetBSD runs because there
isn't a simple binary that just runs the executable.

We now create an additional binary `linux_fcntl` for testing this
since there are header conflicts when including all necessary headers.
This binary is run on all platforms even though it's empty on all non-
Android/non-Linux platforms.

Testing has been switched from a custom binary to using a runner-less
test (or pair of tests). This means that for local development a simple
`cd libc-test && cargo test` will run all the tests. CI has also been
updated here to reflect that.

It's now broken due to changes in the `gcc` crate and having a too-old compiler,
and in general it's unfortunately architecturally so different from the other
test frameworks that it's difficult to maintain over time.

We can't test s390x because qemu segfaults but we can at least verify that it
compiles.

Closes #650