Use Reqwest backend for Appveyor, not Hyper which is deprecated

Since https://github.com/rust-lang-nursery/rustup.rs/pull/1222 Appveyor builds have been complaining, so should stop asking for the Hyper backend

Factor out platforms for which libc is empty

This change shouldn't change any functionality. It just separates the platforms for which `libc` is currently empty (only `wasm32-unknown-unknown`), from those for which it isn't. This is a non-functional change.

Formatting and shellcheck

Add chflags(2) and friends

Use OR in the license field

According to [The Manifest Format](https://doc.rust-lang.org/cargo/reference/manifest.html):
>Multiple licenses can be separated with a `/`, although that usage is deprecated.  Instead, use a license expression with AND and OR operators to get more explicit semantics.

the f macro is unused in some targets

Add support for SIGSYS in signalfd

Android's NDK typedefs __u64 as unsigned long long.

Linux 4.18 added support for SIGSYS info in signalfd. Add the new
fields to signalfd_siginfo.

While the kernel has support for these new fields now, no libc has
shipped a release with the new signalfd fields.

NetBSD: these extattr functions are not in libutil, but libc

 - extattr_namespace_to_string()
 - extattr_string_to_namespace()

Add F_RDLCK/F_WRLCK/F_UNLCK to several platforms

These are used by the flock wrapper in rustc_data_structures. The constants were already present in x86_64-linux-gnu and BSD (since 4928bd98).

Currently the `flock` wrapper in `rustc_data_structures` does not work on several 32-bit musl targets, because they expect the `LARGEFILE64` version of the `F_SETLK`/`F_SETLKW` constants. This PR is a prerequisite to converting that code to use the `libc` types and constants, instead of (inaccurately) duplicating them, since `libc` already provides architecture-specific definitions of the relevant constants.

 - extattr_namespace_to_string()
 - extattr_string_to_namespace()

These are used by the flock wrapper in rustc_data_structures. The
constants were already present in x86_64-linux-gnu and BSD (since
4928bd98).

NetBSD: fix extattr_set_* return types

On FreeBSD and Dragonfly, don't unnecessarily link to libutil

Also, alphabetize this section, since I'm merging two sections anyway.

Fixes #1113

NetBSD: fix pthread types on arm and powerpc

Bump ctest from 0.2.4 to 0.2.6

Bumps [ctest](https://github.com/alexcrichton/ctest) from 0.2.4 to 0.2.6.
- [Release notes](https://github.com/alexcrichton/ctest/releases)
- [Commits](https://github.com/alexcrichton/ctest/commits

)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Also, alphabetize this section, since I'm merging two sections anyway.

Fixes #1113

Add extattr(2) and extattr(3) definitions for FreeBSD and NetBSD

DragonflyBSD does define 3 of these 14 functions.  But I elected not to
add it to the PR because I can't find any evidence that these syscalls
are used on Dragonfly, even in the base system.  And by themselves,
those three are insufficient for the xattr crate.

This bug was never diagnosed.  Perhaps it's been resolved by a newer
compiler.
Fixes #856

DragonflyBSD does define 3 of these 14 functions.  But I elected not to
add it to the PR because I can't find any evidence that these syscalls
are used on Dragonfly, even in the base system.  And by themselves,
those three are insufficient for the xattr crate.

Add CMSG macros for unix/bsd and unix/notbsd

This adds the ["Ancillary Data Object Macros" from RFC 2292](https://tools.ietf.org/html/rfc2292#section-4.3). My C's weak but I think I've translated them faithfully. Tested on macOS and Linux/glibc.

update osx builds to xcode10