Optimizing: Tag arena allocations in SsaBuilder.

Replace GrowableArray with ArenaVector in SsaBuilder and
tag allocations with a new arena allocation type.

Change-Id: I27312c51d7be9d2ad02a974cce93b365c65c5fc4
diff --git a/runtime/base/arena_allocator.h b/runtime/base/arena_allocator.h
index 8104978..c5eb741 100644
--- a/runtime/base/arena_allocator.h
+++ b/runtime/base/arena_allocator.h
@@ -84,6 +84,7 @@
   kArenaAllocEnvironment,
   kArenaAllocEnvironmentVRegs,
   kArenaAllocEnvironmentLocations,
+  kArenaAllocSsaBuilder,
   kArenaAllocMoveOperands,
   kArenaAllocCodeBuffer,
   kArenaAllocStackMaps,