Add support for gdb remote $X stop notification.

debugserver now returns $X09 as the immediate response to
a $k kill process request rather than $W09.

ProcessGDBRemote now properly handles X as indication of
a process exit state.

The @debugserver_test and @lldb_test for $k now properly expects
an X notification (signal-caused exit) after killing a just-attached
inferior that was still in the stopped state.

llvm-svn: 209108
diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
index 8edc554..b79a697 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
@@ -1799,6 +1799,7 @@
         break;
 
     case 'W':
+    case 'X':
         // process exited
         return eStateExited;