This is inital work necessary for diversification support in Subzero.
The random number generator implementation is temporary. It will
eventually use a cryptographically secure pseudorandom number
generator (perhaps from LLVM, if LLVM gets one).
Add the -rng-seed= option to seed the random number generator from
the command line.
BUG=none
R=stichnot@chromium.org
Review URL: https://codereview.chromium.org/455593004
