Return correct name for libgraal-specific collection policy.

Author: christianhaeubl

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/LibGraalCollectionPolicy.java

@@ -65,6 +65,11 @@ public static final class Options {
     private UnsignedWord sizeBefore = Word.zero();
     private GCCause lastGCCause = null;
 
+    @Override
+    public String getName() {
+        return "libgraal";
+    }
+
     /**
      * The hinted GC will be triggered only if the used bytes in eden space is greater than
      * {@link Options#ExpectedEdenSize}, or if the ratio of used bytes to total allocated bytes of