8058235: identify GCs initiated to update allocation context stats

Reviewed-by: mikael, sjohanss

hotspot/src/share/vm/gc_interface/gcCause.hpp

@@ -47,6 +47,7 @@ class GCCause : public AllStatic {
     _heap_inspection,
     _heap_dump,
     _wb_young_gc,
+    _update_allocation_context_stats,
 
     /* implementation independent, but reserved for GC use */
     _no_gc,