These constants have already been deprecated for a few releases with
a deprecation notice, so they can finally be removed.

Closes rust-lang/libc#665

sigevent structs on most platforms have padding or unused fields. Rather
than display those in the Debug impl by deriving it, manually implement
all extra_traits instead ignoring those fields.

This commits adds a second FreeBSD 12 build job,
and splits the implementation of the FreeBSD module
into two modules, one for FreeBSD 11, and one for FreeBSD 12.

The FreeBSD 11 module is compiled always by default, and is
mostly forward compatible with FreeBSD 12 systems.

The FreeBSD 12 module is only built for now in libc's CI,
and uses FreeBSD 12 data types and APIs, linking to symbols
that are only available in FreeBSD 12.

Basically, when LIBC_CI env variable is defined, and the host
system is a FreeBSD 12 system, then the FreeBSD 12 module is
automatically built and tested. Conditional compilation is done
using a `cfg(freebsd12)` flag.

This commit also re-enables many tests, and documents why
some remain disabled.

This was not compile-tested on all platforms, but instead all `pub enum`
types had a `Debug` impl derived for them.

dragonflybsd still uses c_char [2]

[1] https://svnweb.freebsd.org/base/releng/11.2/sys/sys/signal.h?revision=334459&view=markup#l438
[2] https://github.com/DragonFlyBSD/DragonFlyBSD/blob/master/sys/sys/signal.h#L339

PR #1098 added the CMSG_DATA(3) family of functions into libc.  Because
they're defined as macros in C, they had to be rewritten as Rust
functions for libc.  Also, they can't be tested in CI for the same
reason.  But that PR erroneously used the same definitions in BSD as in
Linux.

This commit corrects the definitions for OSX, FreeBSD, DragonflyBSD,
OpenBSD, and NetBSD.  I renamed a few variables and collapsed a few
macros in order to combine the definitions where possible.

Fixes #1210

On FreeBSD, uname is an inline function.  The uname that is present in
libc.so is for FreeBSD 1.0 compatibility.  It expects a buffer of a
different size.

Fixes #1190
Reported-by: Alex Zepeda

These errno's are defined in <sys/errno.h> on DragonFlyBSD.

Signed-off-by: Levente Kurusa <lkurusa@acm.org>

* Added ptrace and constants for all freebsdlike and netbsdlike OSs

Note that OpenBSD and OSX do not support POSIX message queues.

This reverts commit c124acba.

Add network interface flag constants for all platforms.

Rebase of #610 and also move emscripten up much higher in the hierarchy to
ensure that it doesn't have too much of a ripple effect on other platforms.

This involved moving down a good number of definitions, but hopefully was done
with care to not break anything!

This is probably related to cargo failing on DragonFly when running with
multiple jobs.

The minimum pthread stack size has been increase as shown here [1],
which was needed to fix nodejs.

[1]: http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/592912cde1dc358bf080ae9aff3eca491688f47c