Changes due to code review and new implementation:

* Don't use std::string for the function names, const char* will suffice
* Allow each CallOptimizer to validate the function signature before
  doing anything
* Repeatedly loop over the functions until an iteration produces
  no more optimizations. This allows one optimization to insert a
  call that is optimized by another optimization.
* Implement the ConstantArray portion of the StrCatOptimization
* Provide a template for the MemCpyOptimization
* Make ExitInMainOptimization split the block, not delete everything
  after the return instruction.
(This covers revision 1.3 and 1.4, as the 1.3 comments were botched)

llvm-svn: 21548