Clean-up warnings on Linux/GCC

llvm-svn: 217862
diff --git a/lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp b/lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp
index f362477..c237b8d 100644
--- a/lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp
+++ b/lldb/source/Plugins/Process/Linux/NativeThreadLinux.cpp
@@ -113,6 +113,7 @@
         }
         return false;
     }
+    llvm_unreachable("unhandled StateType!");
 }
 
 lldb_private::NativeRegisterContextSP