build failing on openbsd/armv5

[stuartnelson3]

this commit broke the dragonfly build:

golang/sys@9a7256c

check it out and see how to fix it

Currently broken on openbsd/armv5

[stuartnelson3]

golang/go#20055

[stuartnelson3]

The process to contribute to the go repo is ... prohibitive. I committed the fix directly here and am waiting for someone to do golang/go#20055.

e9cb88e

[stuartnelson3]

Now it's failing on openbsd-armv5:

# openbsd-armv5

>> building binaries

 >   alertmanager

 >   amtool

# github.com/prometheus/alertmanager/vendor/golang.org/x/sys/unix

/go/src/github.com/prometheus/alertmanager/vendor/golang.org/x/sys/unix/flock.go:18: undefined: Flock_t

/go/src/github.com/prometheus/alertmanager/vendor/golang.org/x/sys/unix/sockcmsg_unix.go:36: undefined: Cmsghdr

/go/src/github.com/prometheus/alertmanager/vendor/golang.org/x/sys/unix/sockcmsg_unix.go:42: undefined: Cmsghdr

!! command failed: build -o .build/openbsd-armv5/amtool -ldflags -X github.com/prometheus/alertmanager/vendor/github.com/prometheus/common/version.Version=0.5.1 -X github.com/prometheus/alertmanager/vendor/github.com/prometheus/common/version.Revision=e9cb88e15a3b28cb6c0afa3f20ef34a1edb12140 -X github.com/prometheus/alertmanager/vendor/github.com/prometheus/common/version.Branch=master -X github.com/prometheus/alertmanager/vendor/github.com/prometheus/common/version.BuildUser=root@d6492630dae2 -X github.com/prometheus/alertmanager/vendor/github.com/prometheus/common/version.BuildDate=20170421-14:39:39  -extldflags '-static' -a -tags netgo github.com/prometheus/alertmanager/cmd/amtool: exit status 2

To reproduce locally:

# make PREFIX=. GOOS=openbsd GOARCH=arm build

[stuartnelson3]

Fixed by #732