dev-lang/go: Add go ebuild for arm64

A temporary ebuild that builds the go compiler from the latest git
checkout to get support for arm64 builds.  Once go-1.5 is availilable
upstream and merged to portage-stable this ebuild can be removed.

Signed-off-by: Geoff Levand <geoff@infradead.org>

sdk_container/src/third_party/coreos-overlay/dev-lang/go/go-9999.ebuild

@@ -0,0 +1,106 @@
+# Copyright 1999-2015 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+# $Header:  $
+
+EAPI=5
+
+inherit eutils toolchain-funcs
+
+EGIT_REPO_URI="git://github.com/golang/go.git"
+inherit git-r3
+KEYWORDS="-* ~amd64 arm64"
+
+DESCRIPTION="A concurrent garbage collected and typesafe programming language"
+HOMEPAGE="http://www.golang.org"
+
+LICENSE="BSD"
+SLOT="0"
+IUSE=""
+
+DEPEND=""
+RDEPEND=""
+
+# The tools in /usr/lib/go should not cause the multilib-strict check to fail.
+QA_MULTILIB_PATHS="usr/lib/go/pkg/tool/.*/.*"
+
+# The go language uses *.a files which are _NOT_ libraries and should not be
+# stripped.
+STRIP_MASK="/usr/lib/go/pkg/linux*/*.a /usr/lib/go/pkg/freebsd*/*.a /usr/lib/go/pkg/darwin*/*.a"
+
+build_arch()
+{
+    case "$CBUILD" in
+        aarch64*)   echo arm64;;
+        x86_64*)    echo amd64;;
+    esac
+}
+
+same_arch()
+{
+	[[ "${ARCH}" = "$(build_arch)" ]]
+}
+
+src_prepare()
+{
+
+	epatch_user
+}
+
+src_compile()
+{
+	export GOOS="linux"
+	export GOARCH="${ARCH}"
+	export GOROOT_BOOTSTRAP="/usr/lib/go1.4"
+	export GOROOT_FINAL="${EPREFIX}"/usr/lib/go
+	export GOROOT="$(pwd)"
+	export GOBIN=${GOROOT}/bin
+
+	cd src
+	./make.bash || die "build failed"
+}
+
+src_test()
+{
+	$(same_arch) || return 0;
+
+	cd src
+	PATH="${GOBIN}:${PATH}" \
+		./run.bash --no-rebuild --banner || die "tests failed"
+}
+
+src_install()
+{
+	local bin_path
+
+	if $(same_arch); then
+		bin_path=${GOBIN}
+	else
+		bin_path=${GOBIN}/${GOOS}_${GOARCH}
+	fi
+
+	dobin ${bin_path}/*
+	dodoc AUTHORS CONTRIBUTORS PATENTS README.md
+
+	dodir /usr/lib/go
+	insinto /usr/lib/go
+
+	# There is a known issue which requires the source tree to be installed [1].
+	# Once this is fixed, we can consider using the doc use flag to control
+	# installing the doc and src directories.
+	# [1] https://golang.org/issue/2775
+	doins -r doc lib pkg src
+	fperms -R +x /usr/lib/go/pkg/tool
+}
+
+pkg_postinst()
+{
+	# If the go tool sees a package file timestamped older than a dependancy it
+	# will rebuild that file.  So, in order to stop go from rebuilding lots of
+	# packages for every build we need to fix the timestamps.  The compiler and
+	# linker are also checked - so we need to fix them too.
+	ebegin "fixing timestamps to avoid unnecessary rebuilds"
+	tref="usr/lib/go/pkg/*/runtime.a"
+	find "${EROOT}"usr/lib/go -type f \
+		-exec touch -r "${EROOT}"${tref} {} \;
+	eend $?
+}