run time error when building the etcd about docs HOT 3 CLOSED

$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.3 LTS
Release:	16.04
Codename:	xenial
$ go version
go version go1.9.2 linux/s390x
$ git clone https://github.com/coreos/etcd.git
Cloning into 'etcd'...
remote: Counting objects: 70736, done.
remote: Compressing objects: 100% (33/33), done.
remote: Total 70736 (delta 15), reused 19 (delta 8), pack-reused 70695
Receiving objects: 100% (70736/70736), 33.96 MiB | 13.39 MiB/s, done.
Resolving deltas: 100% (44599/44599), done.
Checking connectivity... done.
$ cd etcd/
$ ./build
$ ETCD_UNSUPPORTED_ARCH=s390x ./bin/etcd
2018-01-09 09:34:55.211675 W | etcdmain: running etcd on unsupported architecture "s390x" since ETCD_UNSUPPORTED_ARCH is set
2018-01-09 09:34:55.211925 I | etcdmain: etcd Version: 3.3.0+git
2018-01-09 09:34:55.211931 I | etcdmain: Git SHA: 9bd9d20
2018-01-09 09:34:55.211934 I | etcdmain: Go Version: go1.9.2
2018-01-09 09:34:55.211937 I | etcdmain: Go OS/Arch: linux/s390x
2018-01-09 09:34:55.211940 I | etcdmain: setting maximum number of CPUs to 8, total number of available CPUs is 8
2018-01-09 09:34:55.211951 W | etcdmain: no data-dir provided, using default data-dir ./default.etcd
2018-01-09 09:34:55.212231 I | embed: listening for peers on http://localhost:2380
...