* Don't depend on "guessing" what a FILE* is, just require that the actual

  type be obtained from a CallInst we're optimizing.
* Make it possible for getConstantStringLength to return the ConstantArray
  that it extracts in case the content is needed by an Optimization.
* Implement the strcmp optimization
* Implement the toascii optimization

This pass is now firing several to many times in the following MultiSource
tests:

Applications/Burg      -   7 (strcat,strcpy)
Applications/siod      -  13 (strcat,strcpy,strlen)
Applications/spiff     - 120 (exit,fputs,strcat,strcpy,strlen)
Applications/treecc    -  66 (exit,fputs,strcat,strcpy)
Applications/kimwitu++ -  34 (strcmp,strcpy,strlen)
Applications/SPASS     - 588 (exit,fputs,strcat,strcpy,strlen)

llvm-svn: 21626