Changes From Review Feedback:

* Have the SimplifyLibCalls pass acquire the TargetData and pass it down to
  the optimization classes so they can use it to make better choices for
  the signatures of functions, etc.
* Rearrange the code a little so the utility functions are closer to their
  usage and keep the core of the pass near the top of the files.
* Adjust the StrLen pass to get/use the correct prototype depending on the
  TargetData::getIntPtrType() result. The result of strlen is size_t which
  could be either uint or ulong depending on the platform.
* Clean up some coding nits (cast vs. dyn_cast, remove redundant items from
  a switch, etc.)
* Implement the MemMoveOptimization as a twin of MemCpyOptimization (they
  only differ in name).

llvm-svn: 21569