re PR libgcj/22211 ([4.0 only] Thread.interrupt sometimes causes abort if thread is already dead)

PR libgcj/22211:
	* testsuite/libjava.lang/pr22211.java: New file.
	* java/lang/natThread.cc (finish_): Synchronize when updating
	alive_flag.
	(_Jv_AttachCurrentThread): Likewise.
	(interrupt): Only call _Jv_ThreadInterrupt if thread is alive.
	* java/lang/Thread.java (isAlive): Now synchronized.

From-SVN: r101430

libjava/testsuite/libjava.lang/pr22211.java

@@ -0,0 +1,8 @@
+public class pr22211
+{
+  public static void main(String[] args)
+  {
+    Thread x = new Thread();
+    x.interrupt();
+  }
+}