Three changes:
1. Convert signed integer types to signless versions.
2. Implement the @sext and @zext parameter attributes. Previously the
   type of an function parameter was used to determine whether it should
   be sign extended or zero extended before the call. This information is
   now communicated via the function type's parameter attributes.
3. The interface to LowerCallTo had to be changed in order to accommodate
   the parameter attribute information. Although it would have been
   convenient to pass in the FunctionType itself, there isn't always one
   present in the caller. Consequently, a signedness indication for the
   result type and for each parameter was provided for in the interface
   to this method. All implementations were changed to make the adjustment
   necessary.

llvm-svn: 32788