Adding an annotation that gets to the backend

I wanted to mark certain functions for further processing in the back-end, so I needed to add an annotation that made it through clang. The offical docs on how to add an attribute don't have everything you need to get it passed through to llvm. What I have here starts with what is in the official doc and then adds the extra stuff to get it passed to the backedn.

(All paths to source files are relative to $LLVMBASE

Next into llvm, so it can be parsed and written out as a .bc