x/build/env/illumos-amd64-joyent: add illumos builder

[bradfitz]

Now that we support GOOS=illumos (#20603), it needs a builder.

(Arguably it needed one before we accepted the port.)

We can just set one up on Joyent for now, even if it's not ideal (our plan is to move it to GCE eventually: #15581

So, I uploaded a bootstrap tarball from Linux:

bradfitz@go:~/go/src$ GOOS=illumos GOARCH=amd64 BOOTSTRAP_FORMAT=mintgz ./bootstrap.bash 
...
...
Writing gobootstrap-illumos-amd64-e883d000f4.tar.gz ...
-rw-r--r-- 1 bradfitz bradfitz 51647155 May 29 17:24 /home/bradfitz/gobootstrap-illumos-amd64-e883d000f4.tar.gz

bradfitz@go:~/go/src$ go instal golang.org/x/build/cmd/upload

bradfitz@go:~/go/src$ upload --file=/home/bradfitz/gobootstrap-illumos-amd64-e883d000f4.tar.gz --public go-builder-data/gobootstrap-illumos-amd64-e883d000f4.tar.gz

Then created a new SmartOS VM on Joyent.

Then sshed into it:

bradfitz@go:~$ ssh -i ~/.ssh/id_rsa_golang2 72.2.113.76
...
$ curl -O https://storage.googleapis.com/go-builder-data/gobootstrap-illumos-amd64-e883d000f4.tar.gz
$ mkdir goboot
$ cd goboot
$ tar -zxvf ../gobootstrap-illumos-amd64-e883d000f4.tar.gz 
$ pkgin in gcc47

Now to do more of the steps from https://github.com/golang/build/tree/master/env/solaris-amd64/joyent

/cc @dmitshur

[bradfitz]

# rm /opt/local/sbin/mysqld
# rm /opt/local/sbin/httpd
# cat > /root/.gobuildkey-host-illumos-amd64-joyent
xxxx
^D
# curl -o /opt/buildlet-stage0 https://storage.googleapis.com/go-builder-data/buildlet-stage0.illumos-amd64

[gopherbot]

Change https://golang.org/cl/179418 mentions this issue: all: add illumos/amd64 builder on Joyent

[gopherbot]

Change https://golang.org/cl/179618 mentions this issue: dashboard: update illumos $PATH to include gcc