Golang devtools: Iterate on our default ldflags

[bendiknesbo]

By default, our ldflags sets some unexported variables in an internal/version package, which means it's not easy to e.g. log it during startup.

We should also reconsider which variables we really want, where we want them places (or how to configure other locations), and if we want to use ldflags at all, instead of -buildvcs=true.

[nhhagen]

@bendiknesbo can you follow up on this