They're actually intentionally absent, for a number of reasons.
Yes, you can use a fancier build system if you need something fancy. But the design is such that "go get/install/build" are predictable.
There's talk of adding a "go gen" subcommand to build auto-generated deps in Go 1.4, but it would be an explicit action for package maintainers only, and the generated code would be submitted. It would never run upon go get/install/build.
There's also talk of adding resource embedding as a built-in concept in Go 1.4, as well.