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

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

llvm-svn: 210835
diff --git a/llvm/lib/Support/GraphWriter.cpp b/llvm/lib/Support/GraphWriter.cpp
index 306f3e8..e68ee43 100644
--- a/llvm/lib/Support/GraphWriter.cpp
+++ b/llvm/lib/Support/GraphWriter.cpp
@@ -68,7 +68,7 @@
 std::string llvm::createGraphFilename(const Twine &Name, int &FD) {
   FD = -1;
   SmallString<128> Filename;
-  error_code EC = sys::fs::createTemporaryFile(Name, "dot", FD, Filename);
+  std::error_code EC = sys::fs::createTemporaryFile(Name, "dot", FD, Filename);
   if (EC) {
     errs() << "Error: " << EC.message() << "\n";
     return "";