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

tools/llvm-profdata/llvm-profdata.cpp

@@ -24,6 +24,7 @@
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
+using std::error_code;
 
 static void exitWithError(const Twine &Message, StringRef Whence = "") {
   errs() << "error: ";