Remove all uses of 'using std::error_code' from headers.

llvm-svn: 210866
diff --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h
index 53cf8f9..b848833 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h
@@ -20,11 +20,9 @@
 using namespace llvm;
 
 namespace llvm {
-using std::error_code;
-
 namespace {
 // Helper for extensive error checking in debug builds.
-error_code Check(error_code Err) {
+std::error_code Check(std::error_code Err) {
   if (Err) {
     report_fatal_error(Err.message());
   }