swift234

Introduce the fast runtime ABI for x86_64

This fast ABI both relaxes and constrains the normal x86_64 ABI to
enable fast getter/setter APIs. This ABI is compatible with compilers
that only implement the standard ABI.

Present uses:

  * memory allocation/deallocation
  * strong reference counting

Future uses:

  * weak reference counting
  * reader/writer locks
  * task queues
  * semaphores
  * etc

Swift SVN r2015