swr/rast: Initial work for debugging support.

swr/rast: Initial work for debugging support.

Adds ability to step into jitted llvm IR in Visual Studio.
- Updated llvm type generation script to also generate corresponding debug types.
- New module pass inserts debug metadata into the IR for each function

Disabled by default.

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>