Simplify reporting of undefined symbols.

llvm-svn: 247016
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index 0dc4f60..39c7aa5 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -327,7 +327,8 @@
       Out = BSSSec;
       break;
     case SymbolBody::UndefinedKind:
-      assert(Body->isWeak() && "Should be defined by now");
+      if (!Body->isWeak())
+        error(Twine("undefined symbol: ") + Name);
     case SymbolBody::DefinedAbsoluteKind:
       break;
     case SymbolBody::LazyKind: