docs: def diagnostics(self):
          'Log some system diagnostics before/after setup for ease of debugging'
          # The builder's repr is not used in a command to avoid pointlessly
          # invalidating Docker's build cache.
          return self.step('Diagnostics', [
              self.comment('Builder {0}'.format(repr(self))),
              self.run(ShellQuoted('hostname')),
              self.run(ShellQuoted('cat /etc/issue || echo no /etc/issue')),
              self.run(ShellQuoted('g++ --version || echo g++ not installed')),
              self.run(ShellQuoted('cmake --version || echo cmake not installed')),
          ])