dashboard/env: add gccgo amd64 builder

LGTM=bradfitz
R=bradfitz
CC=adg, golang-codereviews
https://golang.org/cl/139250043

dashboard/env/linux-x86-gccgo/Dockerfile

@@ -0,0 +1,23 @@
+# Copyright 2014 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+# gobuilders/linux-x86-gccgo for 64-bit gccgo.
+
+FROM gobuilders/linux-x86-base
+MAINTAINER golang-dev <golang-dev@googlegroups.com>
+
+ENV DEBIAN_FRONTEND noninteractive
+
+# For using numeric libraries within GCC.
+RUN apt-get install -y --no-install-recommends libgmp10-dev libmpc-dev libmpfr-dev
+
+# For building binutils and gcc from source.
+RUN apt-get install -y --no-install-recommends make g++ flex bison
+
+# gccgo uses the Gold linker from binutils.
+ENV BINUTILS_VERSION binutils-2.24
+RUN curl -s http://ftp.gnu.org/gnu/binutils/$BINUTILS_VERSION.tar.gz | tar x --no-same-owner -zv
+RUN mkdir binutils-objdir
+RUN cd binutils-objdir && ../$BINUTILS_VERSION/configure --enable-gold --enable-plugins --prefix=/opt/gold
+RUN cd binutils-objdir && make -sj && make install -sj

dashboard/env/linux-x86-gccgo/Makefile

@@ -0,0 +1,9 @@
+# Copyright 2014 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+docker: Dockerfile
+	docker build -t gobuilders/linux-x86-gccgo .
+
+docker-linux.gccgo.tar.gz: docker
+	docker save gobuilders/linux-x86-gccgo | gzip | (cd ../../coordinator/buildongce && go run create.go --write_object=go-builder-data/docker-linux.gccgo.tar.gz)

dashboard/env/linux-x86-gccgo/README

@@ -0,0 +1,6 @@
+$ export BUILD=linux-amd64-gccgo
+$ export BUILDREV=6b61234c2552
+$ docker run \
+    -v $HOME/keys/$BUILD.buildkey:/.gobuildkey \
+    gobuilders/linux-x86-gccgo \
+    /usr/local/bin/builder -tool=gccgo -dashboard='https://build.golang.org/gccgo' -rev=$BUILDREV -buildroot=/gccgo -v -cmd='make check-go -kj' $BUILD