Add usleep for Thread::Unregister

Prevent possible bad behavior for realtime threads.

Bug: 111277984
Test: make

Change-Id: Ib558a4e1289675f88ef4d999277287e4dd7ed6d3
diff --git a/runtime/thread_list.cc b/runtime/thread_list.cc
index ba333f6..9222024 100644
--- a/runtime/thread_list.cc
+++ b/runtime/thread_list.cc
@@ -1476,6 +1476,9 @@
         list_.remove(self);
         break;
       }
+      // In the case where we are not suspended yet, sleep to leave other threads time to execute.
+      // This is important if there are realtime threads. b/111277984
+      usleep(1);
     }
     // We failed to remove the thread due to a suspend request, loop and try again.
   }