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/Transforms/Scalar/SampleProfile.cpp

@@ -51,6 +51,7 @@
 #include <cctype>
 
 using namespace llvm;
+using std::error_code;
 
 #define DEBUG_TYPE "sample-profile"
 

lib/Transforms/Scalar/SimplifyCFGPass.cpp

@@ -36,6 +36,7 @@
 #include "llvm/Pass.h"
 #include "llvm/Transforms/Utils/Local.h"
 using namespace llvm;
+using std::error_code;
 
 #define DEBUG_TYPE "simplifycfg"
 

lib/Transforms/Utils/SpecialCaseList.cpp

@@ -31,6 +31,7 @@
 #include <utility>
 
 namespace llvm {
+using std::error_code;
 
 /// Represents a set of regular expressions.  Regular expressions which are
 /// "literal" (i.e. no regex metacharacters) are stored in Strings, while all