Require members of llvm.used to be named.

The effect of llvm.used is to introduce an invisible reference, so this seems
a reasonable restriction. It will be used to provide an easy ordering of
the entries in llvm.used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183743 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/Verifier.cpp

@@ -467,6 +467,7 @@ void Verifier::visitGlobalVariable(GlobalVariable &GV) {
           Assert1(
               isa<GlobalVariable>(V) || isa<Function>(V) || isa<GlobalAlias>(V),
               "invalid llvm.used member", V);
+          Assert1(V->hasName(), "members of llvm.used must be named", V);
         }
       }
     }