[PATCH] Adding diversity for security

[JF Bastien]

  I discussed this change with the UCI folks offline: the PNaCl team is interested in their approach (binary diversity) And we'd like to help with the reviews to get this upstream into LLVM.

  The current main point of contention seems to be the RNG. Now that LLVM is slowly moving to C++11 would it be acceptable to use one of <random>'s pseudo-random number generators, and use std::random_device when a random seed is needed? Chandler was asking folks to hold off on using C++11 features for the near future (to make sure the switchover is clean), and I'm not sure <random> is whitelisted, but I'd like to get the discussion going.

   Once we settle the RNG issue we could commit the RNG's state as its own change, and handle NOP insertion in a different change?

http://llvm-reviews.chandlerc.com/D1802