Uses an open thread handle as the ThreadJoinId on Windows.

runtime/bin/thread_linux.cc

Index: runtime/bin/thread_linux.cc
diff --git a/runtime/bin/thread_linux.cc b/runtime/bin/thread_linux.cc
index 7a2a92acdb02c09f2201d7a2f854a85729f2cc30..6ea923ea13675fbb2d3e940c30af0af255a51c92 100644
--- a/runtime/bin/thread_linux.cc
+++ b/runtime/bin/thread_linux.cc
@@ -156,11 +156,6 @@ ThreadId Thread::GetCurrentThreadId() {
 }
 
 
-bool Thread::Join(ThreadId id) {
-  return false;
-}
-
-
 intptr_t Thread::ThreadIdToIntPtr(ThreadId id) {
   ASSERT(sizeof(id) == sizeof(intptr_t));
   return static_cast<intptr_t>(id);