With this change we can run a Docker build in QEMU and build ARM or ARM64 binaries directly on an Intel build machine. This feature already supports building with Docker4Mac (Beta31). So it's easy for a developer to compile and test the Docker binaries locally on his dev machine w/o the need of the target hardware. Another use case would be to run builds on a clound CI like Travis to get an instant feedback loop for PR's, all on a common Intel platform w/o the need to set up the CI system on the target hardware.
Usage: build static Docker binaries for ARM 32-bit
```
DOCKER_ENGINE_OSARCH="linux/arm" make binary
```
Usage: build static Docker binaries for ARM64 aka AARCH64
```
DOCKER_ENGINE_OSARCH="linux/arm64" make binary
```
Signed-off-by: Dieter Reuter <dieter.reuter@me.com>
Instead of being split between three files, let's let `hack/make/.detect-daemon-osarch` be our single source of truth for multiarch detection/vars. Not only does it make it slightly easier to make sure we change everything properly when these bits have to change, but it also makes it so that all bits of `hack/make.sh` (especially `hack/make/.ensure-frozen-images`) work properly outside the context of the `Makefile` on all platforms.
Signed-off-by: Andrew "Tianon" Page <admwiggin@gmail.com>
