Create a more organized (but still commented out as not very useful)

stub for OpenCL work. I can't really dig enough out of the commit log
messages other than to tell that a lot of work went into this in the 2.9
-> 3.0 timeframe. I'll let the folks touching it decide if it merits
a spot in the release notes and provide the appropriate details if so.

llvm-svn: 145291