This updates GoPackage/Build/Compile in golang-package.mk to accept
additional arguments that are passed to the go command line.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

This also changes the bootstrap source URL to the official GitHub
mirror, to make building easier for places where Google sites aren't
accessible. Fixes #6326.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

obfs4proxy is a Tor pluggable transport proxy, implementing obfs4.

This commit also includes obfs4proxy's build time dependencies:

* golang-github-agl-ed25519: Go implementation of Ed25519 signature
  algorithm
* golang-github-dchest-siphash: Go implementation of SipHash-2-4
* golang-golang-x-crypto: Go supplementary cryptography libraries
* golang-golang-x-net: Go supplementary network libraries
* golang-golang-x-sys: Go packages for interaction with the OS
* golang-golang-x-text: Go text processing support
* golang-torproject-pluggable-transports-goptlib: Tor pluggable
  transports library for Go

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

From golang.org:
The Go programming language is an open source project to make
programmers more productive.

This commit consists of two "parts":

* golang/host: Main Go compiler for host (installed to
  STAGING_DIR_HOST/lib/go-cross), used to cross-compile Go programs to
  be packaged.

* golang (and golang-src/golang-doc): Main Go compiler for on-target
  development. These packages are quite large, but I would expect only
  developers to install these.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>