Fix clang errors in ArenaAllocator.

Change-Id: Ib0fa290fd46ff9288f86cda9be2d1c1faf99b964
diff --git a/compiler/utils/arena_allocator.h b/compiler/utils/arena_allocator.h
index a6b74f7..18a5bce 100644
--- a/compiler/utils/arena_allocator.h
+++ b/compiler/utils/arena_allocator.h
@@ -90,6 +90,8 @@
   size_t num_allocations_;
   // TODO: Use std::array<size_t, kNumArenaAllocKinds> from C++11 when we upgrade the STL.
   size_t alloc_stats_[kNumArenaAllocKinds];  // Bytes used by various allocation kinds.
+
+  static const char* kAllocNames[kNumArenaAllocKinds];
 };
 
 typedef ArenaAllocatorStatsImpl<kArenaAllocatorCountAllocations> ArenaAllocatorStats;