Support: Make error_category's constructor public

Since our error_category is based on the std one, we should have the
same visibility for the constructor.  This also allows us to avoid
using the _do_message implementation detail in our own categories.

llvm-svn: 203998
diff --git a/llvm/lib/Object/Error.cpp b/llvm/lib/Object/Error.cpp
index 47ce38c..8e50869 100644
--- a/llvm/lib/Object/Error.cpp
+++ b/llvm/lib/Object/Error.cpp
@@ -18,11 +18,11 @@
 using namespace object;
 
 namespace {
-class _object_error_category : public _do_message {
+class _object_error_category : public error_category {
 public:
-  virtual const char* name() const;
-  virtual std::string message(int ev) const;
-  virtual error_condition default_error_condition(int ev) const;
+  const char* name() const override;
+  std::string message(int ev) const override;
+  error_condition default_error_condition(int ev) const override;
 };
 }