Bump to 0.2.21

closes https://github.com/rust-lang/libc/issues/539

closes https://github.com/rust-lang/libc/issues/539

Adds many socket related constants

Started off adding a few constants to help cleaning up some `nix-rust/nix` issues.  Went a little.. further.

Adds lots of socket-related constants (`PF_*`, `MSG_*`, `AF_*`, `SO_*`, `SOL_*`, etc.) to linux/bsd flavors.

Added constants to `bsd/frebsdlike/dragonfly` for completeness, though they aren't covered by CI.  Did not touch `notbsd/linux/s390x.rs`

Add and fix tests for {i686, aarch64}-linux-android targets

I think that these changes do not breaks compatibility.

There are some types and constants changes to i686 and aarch64, but I see these changes as bug fixes instead of breaking changes. Also the type time64_t was remove from aarch64 because it is not defined in this arch.

Fixes #536

Add OXTABS and ONOEOT for BSD systems

According to all references I could find these are BSD extensions to POSIX and are also supported on OS X.

Add cfmakeraw and cfsetspeed

This includes implementations for Android. `cfsetspeed` is basically just a back-to-back call to `cfsetispeed` and `cfsetospeed`, both of which seem to do the same thing here, so I just copied that body as well for `cfsetspeed`. The implementation for `cfmakeraw` was taken from the man pages for `termios(3)`.

    - Copy 17 functions definitions from src/unix/mod.rs
      to src/unix/bsd/mod.rs src/unix/haiku/mod.rs
      src/unix/notbsd/linux/mod.rs and src/unix/solaris/mod.rs
    - Add some functions to android that was cfged out
    - Remove cf* and tc* functions implementations for android
      (they are available with api >= 12, which was release in 2011)

This includes implementations for Android.

Add ppoll() for all unix platforms

I'm unsure of whether there is support in OS X for this, and I can't find anything online (so I'm betting there isn't), but I'm going to let this run through CI to confirm.

Added baudrate constants.

Addresses #528, adding baudrate constants for `bsd` and `notbsd` flavors of `unix`.

Passes `libc-test` locally on ubuntu 14.04 LTS with the additional (uncommitted) entries into in `build.rs`:

```
cfg.skip_const( move |name| {
        match name {
            # ... snip ...
            "PTRACE_O_SUSPEND_SECCOMP" |
            "CLONE_NEWCGROUP" |
            "NETLINK_LIST_MEMBERSHIPS" |
            "NETLINK_LISTEN_ALL_NSID" |
            "NETLINK_CAP_ACK" |
            "PR_CAP_AMBIENT_CLEAR_ALL" |
            "PR_CAP_AMBIENT_LOWER" |
            "PR_CAP_AMBIENT_RAISE" |
            "PR_CAP_AMBIENT_IS_SET" |
            "PR_CAP_AMBIENT" |
            "PR_FP_MODE_FRE" |
            "PR_FP_MODE_FR" |
            "PR_GET_FP_MODE" |
            "PR_SET_FP_MODE" |
            "PR_MPX_DISABLE_MANAGEMENT" |
            "PR_MPX_ENABLE_MANAGEMENT" |
            "PR_GET_THP_DISABLE" |
            "PR_SET_THP_DISABLE" |
            "PR_SET_MM_MAP_SIZE" |
            "PR_GET_MM_MAP_SIZE" |
            "PR_SET_MM_MAP" |
            "NLM_F_DUMP_FILTERED" |
            "EPOLLEXCLUSIVE" => true,

            _ => false,
        }
    });
```
I'm assuming this is because I'm stuck using `linux-libc-dev:3.13.0-24.46` for the moment and those constants are defined in newer versions.

- some tests are failing
- remove readlink, timegm and sig* functions in favor of the
  unix/mod.rs definitions
- remove time64_t (it is not defined for aarch64)
- move some definitions to android/b32.rs and create appropriated
  definitions in android/b64.rs

```
export TARGET=x86_64-unknown-openbsd
export QEMU=openbsd.qcow2
sh ci/run-docker.sh $TARGET
```
Passes when run localy.

Adding `termios.h` behind `rpcsvc/rex.h` does not solve the #define
clash since `rex.h` also defines the `_SYS_TERMIOS_H_` include guard.

I'm unsure of whether there is support in OS X for this, and I can't find
anything online (I'm betting there isn't), but I'm going to let this run
through CI to confirm

add tmpnam and pthread_exit

tmpnam and readdir are trivial IMO.

About the `pthread_create` change: It needs `unsafe` for passing `C` functions to pthread_create (with rust functions the omission of `unsafe` is working of course).

`bindgen` produces this function definition:

```
pub fn pthread_create(arg1: *mut pthread_t,
                      arg2: *const pthread_attr_t,
                      arg3: Option<unsafe extern "C" fn(arg1: *mut c_void) -> *mut c_void>,
                      arg4: *mut c_void) -> c_int;
```

So it would add an additional `Option` around the function. But that would break existing code which uses `libc::pthread_create` and what use is it to call pthread_create without any function pointer, so I left `Option` out.

For reference: I also opened a [stackoverflow question](http://stackoverflow.com/questions/42284562) where the answers were also suggesting adding `unsafe` to the function definition.