Driver: Add "d" flag to Options.def for options which are completely

handled by driver. 
 - This is not very precise, we use it to drive the "forward-to-gcc"
   predicate, when trying to talk to a generic gcc tool.

 - Slightly better than what ccc was doing, and should be good
   enough. Platforms which want a robust driver should implement a
   proper tool chain.

llvm-svn: 67181