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/IR/Module.cpp

@@ -28,6 +28,7 @@
 #include <cstdarg>
 #include <cstdlib>
 using namespace llvm;
+using std::error_code;
 
 //===----------------------------------------------------------------------===//
 // Methods to implement the globals and functions lists.