Initial set of changes to add a new 'swift_driver' executable.

- Added a couple of new targets:
  - libswiftDriver, which contains most of the driver implementation
  - swift_driver, which produces the actual executable

- Added centralized version information into libswiftBasic.

- Added a new "Driver Design & Internals" document, which currently describes
  the high-level design of the Swift driver.

- Implemented an early version of the functionality of the driver, including
  versions of the Parse, Pipeline, Bind, Translate, and Execute driver stages.
  Parse, Pipeline, and Bind are largely implemented; Translate and Execute are
  early placeholders. (Translate produces "swift_driver --version" and "ld -v"
  commands, while Execute performs all subtasks sequentially, rather than in
  parallel.)

This is just the starting point for the Swift driver. Tests for the existing
behavior are forthcoming.

Swift SVN r10933

include/swift/CMakeLists.txt

@@ -0,0 +1 @@
+add_subdirectory(Driver)