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

llvm-svn: 210866
diff --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
index c1eb0fd..b1558c0 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
@@ -23,6 +23,7 @@
 
 using namespace llvm;
 using namespace llvm::object;
+using std::error_code;
 
 #define DEBUG_TYPE "dyld"