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>
Upstream-commit: 0d7e118f0199102924c318c80b7e7a10720e1874
Component: engine
beb7c759eb