[dev.regabi] cmd/dist: automatically bootstrap cmd subdirs

We want almost all cmd subdirectories anyway, and relative to the cost
of the rest of toolchain bootstrapping, copying/rewriting a few extra
source files is way cheaper than the engineering cost of forgetting to
maintain these lists as we split out new packages.

While here, also add cmd/internal/archive (and make it compile with Go
1.4) because it'll be needed in subsequent refactorings anyway; and
skip files starting with # (emacs temporary files) and test files
ending with _test.go.

Change-Id: Ic86e680a5fdfaecd617c36d5d04413293b2d6f52
Reviewed-on: https://go-review.googlesource.com/c/go/+/279832


Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>