Especially out/buildroot takes ages to "go list".
Literally 5 minutes, for my 16 GB directory...
So list "cmd" and "pkg" explicitly, to avoid "out".
Unfortunately only "vendor" is allowed to exclude.
Instead of running `go list` every time (very slow),
cache the results in the build folder and include it.
Add a shell helper script, to make the Makefile more
readable. Use regular "makedepend" syntax for output.