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

llvm/lib/Object/ObjectFile.cpp

@@ -20,6 +20,7 @@
 
 using namespace llvm;
 using namespace object;
+using std::error_code;
 
 void ObjectFile::anchor() { }