This commit changes most uses of cfg_if as follows:
- fallthrough `else` usage is avoided for architecture or OS specific
  items
- a comment is added in the final `else` clause to signal intent someone
  modifying

It is safer to omit items than include ones for the wrong platform or
architecture.

Run CI on all branches

Only running them against auto-libc unfortunately means that PRs don't run CI.

Only running them against auto-libc unfortunately means that PRs don't run CI.

Prep repo to be bors-compatible

In... theory this is what we need? Let's try it out.

linux: Add SYS_perf_event_open syscall numbers

The associated `perf_event_attr` struct is not included as it contains
unions and a bitfield making it unrepresentable in Rust. Additionally,
it is not entirely stable, and has changed size several times.

apple: Add openpty(3) and forkpty(3)

Bump to 0.2.8

Add MAP_STACK and MAP_HUGETLB entries to MIPS so that the nix crate can be built

Merging more PRs in the queue

When building with musl for an arm target link with a shared libc (like mips
already does).

Merge a few PRs together

Conflicts:
	src/unix/notbsd/linux/musl/b32/arm.rs
	src/unix/notbsd/linux/musl/b32/asmjs.rs
	src/unix/notbsd/linux/musl/b32/x86.rs
	src/unix/notbsd/linux/musl/b64/mod.rs
	src/unix/notbsd/linux/other/b32/x86.rs
	src/unix/notbsd/linux/other/b64/aarch64.rs
	src/unix/notbsd/linux/other/b64/powerpc64.rs
	src/unix/notbsd/linux/other/b64/x86_64.rs

The function is defined in POSIX [0], but according to Gnulib docs [1],
it is missing or not declared on at least some versions of OS X and
FreeBSD. On Solaris, it is not a system call but is present as
fdatasync(3) [2].

[0] http://www.opengroup.org/onlinepubs/9699919799/functions/fdatasync.html
[1] https://www.gnu.org/software/gnulib/manual/html_node/fdatasync.html
[2] http://docs.oracle.com/cd/E36784_01/html/E36874/fdatasync-3c.html

Add SYS_gettid

This is how MetadaExt expects these fields to be named.

See https://github.com/rust-lang/rust/blob/c116ae35cf49b55bd8d82e31f1ba030cf7e63867/src/libstd/os/linux/fs.rs#L107-L121

Use nightlies for iOS and rumprun

iOS was fixed awhile back and we should have rumprun nightlies now, so let's use
them!

It's tough to have PRs bounce or to have a back and forth with contributors
about minor style quibbles. Sometimes it ends up just being easier to fix style
after the fact, but let's add some automation to help this!

This commit adds a script to run on CI and locally to verify the style of this
repository. There's a few stylistic guidelines to ensure that definitions are
understandable across the jungle of modules. This consistency should help assist
readability for any future readers!

Add select() to Android bindings

Rebase a few PRs in the queue