makemac: add systemd service file
makemac: add systemd service file

Fixes golang/go#20224

Change-Id: Ia1639dad1760e120c23dc495d8341dfaee86ff63
Reviewed-on: https://go-review.googlesource.com/46330
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build