Prepare for ARM/FreeBSD/NetBSD nightlies

[alexcrichton]

This commit beefs up Cargo's makefiles to support nightly builds of Cargo for
multiple platforms. This primarily involves vendoring the logic of how to build
OpenSSL for statically linking against Cargo into the Makefiles directly. We'll
have to update the version of OpenSSL as releases are made, but we essentially
already do that with the normal docker container.

The Linux nightlies will still run in the normal dist docker container (a really
old CentOS build) and builds for new platforms will happen in the standard
linux-cross container we use for other cross builds. The nightly versions of
these will produce Cargo tarballs for a whole bunch of platforms to get
uploaded.

This has been tested in the alexcrichton/rust-slave-linux-cross:2016-03-17b
docker container for the 3 ARM targets and FreeBSD target. NetBSD will come once
rust-lang/rust#32407 lands.

[rust-highfive]

r? @huonw

(rust_highfive has picked a reviewer for you, use r? to override)

[alexcrichton]

Some of the makefile/script changes here as well were also done to support out-of-tree build directories (when I was playing around inside docker). The updates of crates were just done largely to add cfg(unix) dependencies (via the new syntax) on openssl-sys, and that's also why the Cargo snapshot has been updated (to a Cargo which understands this syntax).

r? @brson

[alexcrichton]

cc @japaric

[brson]

@bors r+ fuck makefiles

[bors]

📌 Commit d363095 has been approved by brson

[alexcrichton]

@bors: r=brson 83b4f39

[bors]

⌛️ Testing commit 83b4f39 with merge e43adeb...

[bors]

☀️ Test successful - cargo-linux-32, cargo-linux-64, cargo-mac-32, cargo-mac-64, cargo-win-gnu-32, cargo-win-gnu-64, cargo-win-msvc-32, cargo-win-msvc-64