avoid inifinite recursion if java.lang.Object is missing; refactoring

When trying to create an array class, we try to resolve
java.lang.Object so we can use its vtable in the array class.
However, if Object is missing, we'll try to create and throw a
ClassNotFoundException, which requires creating an array to store the
stack trace, which requires creating an array class, which requires
resolving Object, etc..  This commit short-circuits this process by
telling resolveClass not to create and throw an exception if it can't
find Object.

While doing the above work, I noticed that the implementations of
Classpath::makeThrowable in classpath-avian.cpp and
classpath-openjdk.cpp were identical, so I made makeThrowable a
top-level function.

Finally, I discovered that Thread.setDaemon can only be called before
the target thread has been started, which allowed me to simplify the
code to track daemon threads in the VM.

classpath/java/lang/Thread.java

@@ -239,12 +239,12 @@ public class Thread implements Runnable {
   }
 
   public synchronized void setDaemon(boolean v) {
-    if (v != daemon) {
-      setDaemon(this, v);
+    if (getState() != State.NEW) {
+      throw new IllegalStateException();
     }
-  }
 
-  private static native void setDaemon(Thread t, boolean increment);
+    daemon = v;
+  }
 
   public static native void yield();