add JNI_GetCreatedJavaVMs stub

Recent versions of IcedTea will not run unless libjvm.so exports this
symbol.  The quick fix is to provide a stub which just always returns
-1 to indicate an error.  I'll leave a proper implementation for when
we need to support an app that actually uses this function.

src/jnienv.cpp

@@ -3626,6 +3626,13 @@ JNI_GetDefaultJavaVMInitArgs(void*)
   return 0;
 }
 
+extern "C" JNIEXPORT jint JNICALL
+JNI_GetCreatedJavaVMs(Machine**, jsize, jsize*)
+{
+  // todo
+  return -1;
+}
+
 extern "C" JNIEXPORT jint JNICALL
 JNI_CreateJavaVM(Machine** m, Thread** t, void* args)
 {