RFR(XXS): 8236124: Minimal VM slowdebug build failed after JDK-8212160

[serguei.spitsyn at oracle.com]

Please, review a trivial fix for bug:
   https://bugs.openjdk.java.net/browse/JDK-8236124

Patch suggested by A. Shipilev:

diff --git a/src/hotspot/share/code/nmethod.cpp 
b/src/hotspot/share/code/nmethod.cpp
--- a/src/hotspot/share/code/nmethod.cpp
+++ b/src/hotspot/share/code/nmethod.cpp
@@ -1601,7 +1601,7 @@
        ServiceThread::enqueue_deferred_event(&event);
      } else {
        // This enters the nmethod barrier outside in the caller.
-      state->enqueue_event(&event);
+      JVMTI_ONLY(state->enqueue_event(&event));
      }
    }
  }


Summary:
   The slowdebug build was broken by the fix of JDK-8212160 which 
introduced new function: enqueue_event().
   The fix is to call it only if the JVM TI is enabled.

Testing:
   Ran slowdebug build locally.

Thanks,
Serguei