Fix builds on go 1.18

[willgorman]

When building with Go 1.18 I was seeing the following errors that are fixed by this change.

❯ make build
:: building go binary 8.1
CGO_ENABLED=0 go build \
		-ldflags "-X main.version=8.1" \
		-gcflags "-trimpath /Users/will.gorman/go/src"
# golang.org/x/sys/unix
../../go/pkg/mod/golang.org/x/[email protected]/unix/syscall_darwin.1_13.go:25:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.1_13.go:27:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.1_13.go:40:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.go:28:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.go:43:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.go:59:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.go:75:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.go:90:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.go:105:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.go:121:3: //go:linkname must refer to declared function or variable
../../go/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_amd64.go:121:3: too many errors

[kovetskiy]

Thanks!