souper optimization profiling support

this pull req adds redis-based profiling of the dynamic hit count of Souper optimizations in the optimized program

Peter, before doing the makefile integration I wanted to get your feedback on where the new library file belongs.

The other issue is that building a program with Souper profiling is non-transparent since it needs to be linked against our new little library and also hiredis. The easy workaround is to add the necessary code into compiler-rt in the LLVM that we build. This would pull a bit of hiredis code into the souper repo. Is that OK or is it a licensing no-no? I would hope it is OK due to the bsd-style licence:

https://github.com/redis/hiredis/blob/master/COPYING