swift234

[PATCH] [Driver] Add support for using 'swift' to exec subcommands.

 - This allows 'swift <FOO>' to be used to invoke swift-<FOO>, so that we can
   use 'swift' as a namespace for additional commands (like ones used for the
   package manager.

 - This patch just adds the basic subcommand functionality, but doesn't rework
   either 'swift-autolink-extract' or 'swift -frontend' to follow this code path.

 - <rdar://problem/22844530> Provide 'swift' support for subcommands



Swift SVN r32367