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/tools/llvm-objdump/llvm-objdump.cpp

@@ -64,6 +64,7 @@
 
 using namespace llvm;
 using namespace object;
+using std::error_code;
 
 static cl::list<std::string>
 InputFilenames(cl::Positional, cl::desc("<input object files>"),cl::ZeroOrMore);