Don't use 'using std::error_code' in include/llvm.

This should make sure that most new uses use the std prefix.

llvm-svn: 210835
diff --git a/llvm/lib/AsmParser/Parser.cpp b/llvm/lib/AsmParser/Parser.cpp
index ef9328a..1dfcc19 100644
--- a/llvm/lib/AsmParser/Parser.cpp
+++ b/llvm/lib/AsmParser/Parser.cpp
@@ -20,6 +20,7 @@
 #include <cstring>
 #include <system_error>
 using namespace llvm;
+using std::error_code;
 
 Module *llvm::ParseAssembly(MemoryBuffer *F,
                             Module *M,