Don't import make_error_code into the llvm namespace.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210772 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/ErrorOr.h

@@ -99,6 +99,7 @@ public:
                                       std::is_error_condition_enum<E>::value,
                                   void *>::type = 0)
       : HasError(true) {
+    using std::make_error_code;
     new (getErrorStorage()) error_code(make_error_code(ErrorCode));
   }