Add acct(2) to BSD module

The `acct` syscall is supported on BSD platforms, the PR aims to add it to the BSD module.

This patch removes the x86_64-rumprun-netbsd triple from Travis CI.

Arch specific ptrace commands for BSDs

This PR is to add architecture specific ptrace requests etc.

Don't merge this yet if it passes I want to go over the other BSDs and architectures to see if I've missed anything I'm just creating the PR to get that initial CI approval that it's right as I expect this bit to be more fiddly.

Add ptrace for non-apple BSDs

So yesterday I did a PR for ptrace for apple, I've now gone through the ptrace header files for the other BSDs supported by libc and added ptrace + constants for all of them.

Given the lack of ptrace in any of them I don't know if the test has to be changed at all for the new functions so I'll tackle any CI errors that come up if and as they appear.

* Added ptrace and constants for all freebsdlike and netbsdlike OSs

Added ptrace constants for apple

I noticed the ptrace constants were missing for apple so I've added them referencing this [header](https://opensource.apple.com/source/xnu/xnu-792.13.8/bsd/sys/ptrace.h). This doesn't add any new functions just constants so I haven't added any tests which seems to be correct.

Revisit work on cvoid

At the recommendation of @SimonSapin [here](https://github.com/rust-lang/rust/issues/53856#issuecomment-422932721), I have revisited the build script to check whether `core::ffi::c_void` resolves, instead of relying on a particular `rustc` version. This allows use on `1.30.x` builds with `core::ffi::c_void`.

I also noticed that `c_void` is defined twice in this crate, once in `lib.rs` and again in `switch.rs`. This instead defines `c_void` for every target except `wasm32`. As far as I can tell, this shouldn't actually change functionality on any existing targets.

Add ftok on MacOS

Provide a symbol for the `ftok` function declared in sys/ipc.h, for completeness and to allow calling `ftok` to generate the key value for `shmat`.

Add fcntl constants for advisory locking on BSDs

For range-based locking POSIX fcntl locks are needed. This adds the
constants F_RDLCK, F_UNLCK, and F_WRLCK for FreeBSD, NetBSD, OpenBSD,
DragonFlyBSD, and macOS/iOS. Fortunately these values are defined the same across these platforms.

Provide a symbol for the `ftok` function declared in sys/ipc.h, for completeness and to allow calling `ftok` to generate the key value for `shmat`.

For range-based locking POSIX fcntl locks are needed. This adds the
constants F_RDLCK, F_UNLCK, and F_WRLCK for FreeBSD, NetBSD, OpenBSD,
DragonFlyBSD, and macOS/iOS. Fortunately these values are defined the same across these platforms.

Expose futimens and utimensat on FreeBSD and DragonFly

Should have sent this out with #1084 but I didn't notice then that these were missing (see https://github.com/nix-rust/nix/pull/944).

Haven't been able to test these locally as I do not have access to these platforms. Will rely on CI to verify these for me.

Expose futimens and utimensat on Apple platforms

Entries copy/pasted from `netbsdlike/mod.rs`.

Add fallocate64 and posix_fallocate64 bindings

These are necessary for large file support on 32-bit platforms,
following the same pattern as 74825222 ("Add bindings for
-D_FILE_OFFSET_BITS=64").

Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>

These are necessary for large file support on 32-bit platforms,
following the same pattern as 74825222 ("Add bindings for
-D_FILE_OFFSET_BITS=64").

Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>

Re-export core::ffi::c_void if it exists

This is the second part of the implementation of [RFC 2521](https://github.com/rust-lang/rfcs/pull/2521), replacing the definition of `c_void` in libc with a re-export of the type from `core::ffi::c_void` on builds it exists for.

This uses the re-export for rustc version `1.31.0` or greater, as `1.30.x` was the current nightly when [the PR for the changes to libcore and libstd](https://github.com/rust-lang/rust/pull/53910) was merged, so I'm assuming the first nightly they will appear in will be `1.31.0`; is this acceptable?

cc rust-lang/rust#53856

Theoretically test statics

There are none of them in `libc` except for `__progname` on Android, but
that one cannot be tested because it's not present in any header files.

Add new FreeBSD socket option SO_REUSEPORT_LB.

FreeBSD 12, which is scheduled to be released soon, has a new socket option SO_REUSEPORT_LB.
From setsockopt man page:
     SO_REUSEPORT_LB allows completely duplicate bindings by multiple
     processes if they all set SO_REUSEPORT_LB before binding the port.
     Incoming TCP and UDP connections are distributed among the sharing
     processes based on a hash function of local port number, foreign IP
     address and port number. A maximum of 256 processes can share one socket.

Fix mips-unknown-linux-uclibc target

The mips(el)-unknown-linux-uclibc target has apparently been broken in one way or another for over a year. This PR is the patch it took to successfully build a beta toolchain that could support it.

I am pretty sure these fixes are the right answer, after considerable digging in both the libc crate source (_pub-use pub-use everywhere, and not a hint to link_) and the uClibc source (_it's not POSIX, but they've shipped it since 2007, so close enough_).

For those who don't know, the *-uClibc targets are the only way (AFAIK) to create Rust binaries which run on Linux kernels prior to 2.6. It is a use case that is getting quite rare these days, but is still present in embedded ecosystems where chip vendors never migrated their hardware support to newer kernel versions.

Here's hoping these Rust toolchain targets find a maintainer someday.

cc rust-lang/rust#43503

Add a couple more ELF types