commit e8c716005a0538554a5ca9a9d248f7f7c1200a9e
author Asim Shankar <ashankar@google.com> Thu Mar 10 13:38:31 2016 -0800
committer Asim Shankar <ashankar@google.com> Thu Mar 10 13:38:31 2016 -0800
tree 184f5c34d4f34bdf50338cdd1a0f719475136fd3
parent 243b9a8ff962ce589245eca3d44abdc5c6114ca9

jiri-profile-v23: Enable go 1.6 and...

A couple of changes in this patch:
(1) Support for installing a release go toolchain from the official
    release tarball instead of compiling it from scratch.
    Compilation from scratch required that we first build go1.4
    and then the target version. With the release tarball, it's
    one download and untar instead of two downloads and toolchain
    builds.
(2) Use a single toolchain installation across multiple targets if
    possible. As of Go 1.6, a single toolchain is sufficient for
    --target=<hostos>-<hostarch>, --target=arm-android and
    --target=arm-linux
    This sharing allows us to reduce the number of copies of the Go
    toolchain considerably (instead of go1.4+go1.5 compiled for
    each target, there will be one installation of the release go
    toolchain).
    For example, on my laptop:
    - jiri profile-v23 install v23:base && jiri profile-v23 install v23:android
      consumes ~1.2GB in the profiles/go directory before this change
      and will consume 300MB with the shared toolchain,
(3) Set the CC and CXX environment variables.
    Previously, only CC_FOR_TARGET and CXX_FOR_TARGET were being set.
    Those two are needed when building a toolchain and their values
    are compiled into the toolchain as the default compilers for C/C++
    code. Setting CC and CXX allows the same go toolchain to be shared
    across different target platforms since it is the mechanism used
    to set the C/C++ compilers for cgo.
(4) Add a go1.6 version to the go profile

However, the defaults still stay at Go 1.5.1. Some code in Vanadium
(or depended on by Vanadium) still needs to be fixed to work correctly
with Go 1.6, so I'll wait to switch the default version to 1.6 till
then.

Change-Id: I4f52b850b560e7b5577751e6d8c374d3f46e1424