make this more efficient in release builds (time and space)

llvm-svn: 33239
diff --git a/llvm/lib/VMCore/AsmWriter.cpp b/llvm/lib/VMCore/AsmWriter.cpp
index 6f7c495..d5c163f 100644
--- a/llvm/lib/VMCore/AsmWriter.cpp
+++ b/llvm/lib/VMCore/AsmWriter.cpp
@@ -873,11 +873,9 @@
       abort();
     }
     switch (GV->getVisibility()) {
+    default: assert(0 && "Invalid visibility style!");
     case GlobalValue::DefaultVisibility: break;
     case GlobalValue::HiddenVisibility: Out << "hidden "; break;
-    default:
-     cerr << "Invalid visibility style!\n";
-     abort();
     }
   }
   
@@ -982,11 +980,9 @@
       abort();
     }
     switch (F->getVisibility()) {
+    default: assert(0 && "Invalid visibility style!");
     case GlobalValue::DefaultVisibility: break;
     case GlobalValue::HiddenVisibility: Out << "hidden "; break;
-    default:
-     cerr << "Invalid visibility style!\n";
-     abort();
     }
   }