Cycles: Fix static initialization order fiasco

Initialization order of global stats and node types was not strictly
defined and it was possible to have node types initialized first and
stats after that. This will zero out memory which was allocated from
the statistics causing assert failure when de-initializing node types.

intern/cycles/util/util_guarded_allocator.cpp

@@ -19,7 +19,7 @@
 
 CCL_NAMESPACE_BEGIN
 
-static Stats global_stats;
+static Stats global_stats(Stats::static_init);
 
 /* Internal API. */
 

intern/cycles/util/util_stats.h

@@ -23,7 +23,10 @@ CCL_NAMESPACE_BEGIN
 
 class Stats {
 public:
+	enum static_init_t { static_init = 0 };
+
 	Stats() : mem_used(0), mem_peak(0) {}
+	explicit Stats(static_init_t) {}
 
 	void mem_alloc(size_t size) {
 		atomic_add_z(&mem_used, size);