Adding eStopReasonThreadExiting and fixing the handling of this state on Linux.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@170800 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/source/Target/ThreadPlanStepUntil.cpp b/source/Target/ThreadPlanStepUntil.cpp
index 95b0a35..deda7d9 100644
--- a/source/Target/ThreadPlanStepUntil.cpp
+++ b/source/Target/ThreadPlanStepUntil.cpp
@@ -292,6 +292,7 @@
             case eStopReasonSignal:
             case eStopReasonException:
             case eStopReasonExec:
+            case eStopReasonThreadExiting:
                 m_explains_stop = false;
                 break;
             default: