Add TIOCGRS485 and TIOCSRS485 for musl #1094

I need help with adding `TIOCSRS485` and `TIOCSRS485` constants to libc.

Add truncate(2) to Unix platforms

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.