swift234

[Reflection] Start fleshing out the remote mirrors library

- Don't depend on LLVM Support and swiftBasic as this will bring in
  llvmSupport and other heavy dependencies, which we don't build for
  non-host architectures right now anyway.

- Add a reader template that works with the same (albeit somewhat
  clunky) interface in-process with the runtime and remotely, by having
  the memory tool supply a function that will copy data from the remote
  process.

- Add a Buffer type to abstract indirecting pointers in a remote address
  space, which is handled by the memory reader.

- Start sketching out the C remote mirrors interface.