Install all specified architectures

[Gabriel Nützi]

Install all platforms and archs specified in deploy.conf or on command line --platform=darwin/arm64 (multiple times)

<installDir>/bin/
  - darwin/
       - amd64/
       - arm64/
  - freebsd/
  - ...

• githooks.runner needs to point to correct executable on each platform.
• Provide git hook config runner --set --arch arm64 --platform 'darwin' to set it up on other systems
• Run-wrapper cannot know or define the architecture -> bash shit... so we need githooks.runner.
• Installer always sets the --global githooks.runner of the main platform running.