gnu: Add pinball.

* gnu/packages/games.scm (pinball): New variable.
* gnu/packages/patches/pinball-const-fix.patch,
  gnu/packages/patches/pinball-cstddef.patch,
  gnu/packages/patches/pinball-missing-separators.patch,
  gnu/packages/patches/pinball-src-deps.patch,
  gnu/packages/patches/pinball-system-ltdl.patch: New patches.
* gnu-system.am (dist_patch_DATA): Add them.