Since #[cfg] attributes are short-circuting, cfg_if! should not change
the order in which the predicates are listed. This enables the use of
unstable cfg attributes in cfg_if!, which is useful when building libstd.

Fixed for DragonFly

See comments https://github.com/rust-lang/libc/pull/194.

Note on struct utsname: Neither using a constant, nor a conditional
macro seems to work, so I just created an ugly utsname with conditions
on each field. This should also fix the CI fallout. #[cfg] on macros
doesn't work?

As DragonFly only supports one platform, I merged  x86_64.rs into
dragonfly/mod.rs.

Running libc-test: PASSED 3426 tests

commit 1a7ee714db34f17abd33dc9262d3e10275eec68d
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:30:56 2016 +0100

    Fix RLIM_POSIXLOCKS ->  RLIMIT_POSIXLOCKS

commit 09c49a97ebebf087486659ef8277610d99e5c7b3
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:29:24 2016 +0100

    Ignore signedness check for uuid_t on DragonFly

commit aab4d11f59917686280c271683bf00ff34c8040d
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:23:21 2016 +0100

    Move FreeBSD-only function into freebsd/mod.rs

commit 9921f030b103dbccb37930ab1d64cf1dd587bd48
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:21:42 2016 +0100

    Move POSIX_FADV_* to freebsd/mod.rs

commit 2921c2db1e3d0314375aa371936bd227cc6c6e2a
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:20:11 2016 +0100

    Fix signedness of blksize_t for DragonFly

commit 65e817baee9e01d2d7c86c6202c63ee46d218914
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:19:02 2016 +0100

    Fix Q_{GET,SET}QUOTA for DragonFly

commit a0d2d63ef88206d321222140ae6b3d92c93b51bd
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:17:27 2016 +0100

    Fix RLIMIT_* for DragonFly

commit d04a1600a7c66a792a481e1524a1652234a69939
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:12:09 2016 +0100

    Fix ELAST for DragonFly

commit d120b9278426a76ee106e91e6c999885c1f5c7f4
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:10:28 2016 +0100

    Fix F_GETLK, F_SETLK, F_SETLKW for DragonFly

commit 963f7da270a14f4d12ea1a52301e363ce745c897
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:08:51 2016 +0100

    Fix O_CLOEXEC for DragonFly

commit f4d6c9d5991d690c7cb4460790a8e37e713bc034
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:07:18 2016 +0100

    Fix RAND_MAX for DragonFly

commit ba48336da7be613a49702ad9de445ab3850ebb7c
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 13:04:48 2016 +0100

    Fix statvfs for DragonFly

commit 9ae480c60a7d77b31a17d34320464f4179e40a4a
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 12:51:47 2016 +0100

    Fix fd_set for DragonFly

commit a15e027838288c4980371c503252cca7e32356c0
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 12:42:24 2016 +0100

    Fix all remaining issues on DragonFly

    Missing functions and missing constats.

commit 3966e4fce0cb81bd0b3ed8cdf50611e6982f7767
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 12:27:14 2016 +0100

    Use a macro instead of a constant.

    When using a constant, the libc-test thinks this constant
    exists as an C equivalent.

commit 9b5659aaf54419f317250cb3a4692a1c14fdbc33
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 12:21:01 2016 +0100

    Use a constant in utsname

commit 50484eda3c978a9c0a9652f6fc619c41ad349c2d
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 12:17:55 2016 +0100

    Fix struct utsname

commit 832e94248fabc91574d6d42630168da3542c153f
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 12:07:08 2016 +0100

    DragonFly has different stat, dirent, clock_t, ino_t, nlink_t, blksize_t

commit f3152a369d75ae8c1558afa5a59aa55e33b33ec6
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 11:52:54 2016 +0100

    Move DragonFly related stuff into dragonfly/*

    Replicate x86_64.rs from FreeBSD. Need some twists.

commit 9fe35124064aa92303171d019004df119f948223
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 11:49:38 2016 +0100

    Move FreeBSD code under freebsd/*.

    Next commit will replicate some of the architecture dependent stuff
    for DragonFly.

commit e91983df8deb14004f7a0fe47878f0e4eb31198d
Author: Michael Neumann <mneumann@ntecs.de>
Date:   Sat Feb 20 11:44:25 2016 +0100

    struct utsname has a different size on DragonFly

Fix iOS builds

Android: add some of the same LFS functions as Linux

While this appears to be in bionic libc, it's not in any header, so CI
fails to validate it.  Let's just skip that one.

Audit the LFS functions from Linux and add the same for Android if
bionic supports it, according to libc.map from API 23 (Android 6.0).

The standard library is currently limited to API 18, so it may only use
`lseek64`, `pread64`, `pwrite64`, `ftruncate64`, and `readahead`.

Note that `stat64` and `dirent64` are actually identical to the regular
versions, because bionic has always mapped them to the LFS syscalls.
It also sets `O_LARGEFILE` at all times, so `open` matches `open64`.
Still, the explicit LFS names may be useful to match Linux.

Fixes #189.

Roll together a few PRs in the queue

Add `posix_fadvise()` and related constants

Update links in README for transition to rust-lang

PowerPC64 fixes

We no longer need to check for powerpc64le, so remove it.

this fixes the siginfo_t compilation errors

Add a default-on std feature

This adds a `use_std` Cargo feature which disables `#![no_std]` builds of libc,
but is enabled by default. The library will currently continue to link to the
standard library to maintain backwards compatibility with the 0.2 series and
older Rust compilers for now, but this default can possible be changed in the
future.

Rebased again for the latest changes.

The #[cfg()] was looking for 'arget_os' instead of 'target_os'.

Bump to 0.2.7

SIGSTKSZ is the same on OpenBSD, Bitrig, and NetBSD

Rebasing for pull request to be valid.

The #[cfg()] was looking for 'arget_os' instead of 'target_os'.