Run markers before doing garbage collection.

Author: aardvark179

src/main/java/org/truffleruby/core/VMPrimitiveNodes.java

@@ -109,6 +109,7 @@ public static abstract class VMGCStartPrimitiveNode extends PrimitiveArrayArgume
         @TruffleBoundary
         @Specialization
         public DynamicObject vmGCStart() {
+            getContext().getMarkingService().runMarkersAndDropKeptList();
             System.gc();
             return nil();
         }