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/Support/Unix/Memory.inc

@@ -37,6 +37,7 @@ extern "C" void sys_icache_invalidate(const void *Addr, size_t len);
 #else
 extern "C" void __clear_cache(void *, void*);
 #endif
+using std::error_code;
 
 namespace {