Don't use 'using std::error_code' in include/llvm.

This should make sure that most new uses use the std prefix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210835 91177308-0d34-0410-b5e6-96231b3b80d8

lib/ExecutionEngine/Interpreter/Interpreter.cpp

@@ -19,6 +19,7 @@
 #include "llvm/IR/Module.h"
 #include <cstring>
 using namespace llvm;
+using std::error_code;
 
 namespace {