Remove object_error::success and use std::error_code() instead

make_error_code(object_error) is slow because object::object_category()
uses a ManagedStatic variable. But the real problem is that the function is
called too frequently. This patch uses std::error_code() instead of
object_error::success. In most cases, we return "success", so this patch
reduces number of function calls to that function.

http://reviews.llvm.org/D10333

llvm-svn: 239409
diff --git a/llvm/lib/Object/Archive.cpp b/llvm/lib/Object/Archive.cpp
index fb91eed..54ed954 100644
--- a/llvm/lib/Object/Archive.cpp
+++ b/llvm/lib/Object/Archive.cpp
@@ -224,7 +224,7 @@
   child_iterator e = child_end();
 
   if (i == e) {
-    ec = object_error::success;
+    ec = std::error_code();
     return;
   }
 
@@ -254,7 +254,7 @@
     SymbolTable = i;
     ++i;
     FirstRegular = i;
-    ec = object_error::success;
+    ec = std::error_code();
     return;
   }
 
@@ -298,14 +298,14 @@
     StringTable = i;
     ++i;
     FirstRegular = i;
-    ec = object_error::success;
+    ec = std::error_code();
     return;
   }
 
   if (Name[0] != '/') {
     Format = has64SymTable ? K_MIPS64 : K_GNU;
     FirstRegular = i;
-    ec = object_error::success;
+    ec = std::error_code();
     return;
   }
 
@@ -320,7 +320,7 @@
   ++i;
   if (i == e) {
     FirstRegular = i;
-    ec = object_error::success;
+    ec = std::error_code();
     return;
   }
 
@@ -332,7 +332,7 @@
   }
 
   FirstRegular = i;
-  ec = object_error::success;
+  ec = std::error_code();
 }
 
 Archive::child_iterator Archive::child_begin(bool SkipInternal) const {