Assert when range testing G1RefProcDrainInterval on 64-bit systems

The flag G1RefProcDrainInterval is defined like this:
  product(intx, G1RefProcDrainInterval, 10, \
          "The number of discovered reference objects to process before " \
          "draining concurrent marking work queues.") \
          range(1, max_intx)

The value of the flag is used to initialize the an int value in G1CMKeepAliveAndDrainClosure. Since the range is defined to allow max_intx this will fail on 64-bit systems where intx is 64-bits wide.

The test runtime/CommandLine/OptionsValidation/TestOptionsWithRanges doesn't always catch this bug since a concurrent cycle needs to be triggered for the issue to show. To force this we could update the test utils with something like:
diff --git a/test/runtime/CommandLine/OptionsValidation/common/optionsvalidation/JVMOptionsUtils.java b/test/runtime/CommandLine/OptionsValidation/common/optionsvalidation/JVMOptionsUtils.java
--- a/test/runtime/CommandLine/OptionsValidation/common/optionsvalidation/JVMOptionsUtils.java
+++ b/test/runtime/CommandLine/OptionsValidation/common/optionsvalidation/JVMOptionsUtils.java
@@ -216,6 +216,9 @@
             case "CMSPrecleanDenominator":
                 option.addPrepend("-XX:CMSPrecleanNumerator=" + ((new Integer(option.getMin())) - 1));
                 break;
+ case "G1RefProcDrainInterval":
+ option.addPrepend("-XX:+ExplicitGCInvokesConcurrent");
+ break;
             case "InitialTenuringThreshold":
                 option.addPrepend("-XX:MaxTenuringThreshold=" + option.getMax());
                 break;