Subzero: Use a "deterministic" random shuffle for register allocation.

src/IceRNG.h

Index: src/IceRNG.h
diff --git a/src/IceRNG.h b/src/IceRNG.h
index bf01e410d559ffaac0a94fa176f6ff91531cd8bb..a2d8e96fd959bf59c0845103169ec7b2ee1f89f0 100644
--- a/src/IceRNG.h
+++ b/src/IceRNG.h
@@ -53,6 +53,15 @@ private:
   RandomNumberGenerator &RNG;
 };
 
+// RandomShuffle is an implementation of std::random_shuffle() that
+// doesn't change across stdlib implementations.  Adapted from a
+// sample implementation at cppreference.com.
+template <class RandomIt, class RandomFunc>
+void RandomShuffle(RandomIt First, RandomIt Last, RandomFunc &&RNG) {
+  for (auto i = Last - First - 1; i > 0; --i)
+    std::swap(First[i], First[RNG(i + 1)]);
+}
+
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICERNG_H