[llvm-exegesis] Update to cover latency through another opcode.

    Restructuring the code to measure latency and uops.
    The end goal is to have this program spawn another process to deal with SIGILL and other malformed programs. It is not yet the case in this redesign, it is still the main program that runs the code (and may crash).
    It now uses BitVector instead of Graph for performance reasons.

    https://reviews.llvm.org/D46821

    Authored by Guillaume Chatelet

llvm-svn: 332579