This implements the proposal in #2564 and converts a handful of representative
or especially interesting (from a build PoV) packages to use it.
For now those pkg/* affected get a stub-`Makefile`, once all packages are
converted then `pkg/Makefile` can be adjusted and those stubs can be removed.
For now only `pkg/package.mk`'s functionality is implemented. In particular:
- `push-manifest.sh` remains a separate script, to enable calling it on systems
with just the LinuxKit tools installed arrange to install it under a less
generic name.
- `kernel` and `tools/alpine` do not use `pkg/package.mk` and those cases are
not yet fully considered/covered.
I have updated the documentation assuming that the existing uses of
`pkg/package.mk` will be removed quite soon in a follow up PR rather than
trying to document the situation which results after just this commit.
Due to `cmd/linuxkit` now gaining a library the build needs adjusting slightly to
allow both `make bin/linuxkit` and `go build` to work.
`go vet` has forced me to write some rather asinine comments for things that
are rather obvious from the name.
Signed-off-by: Ian Campbell <ijc@docker.com>
