[ELF2] Implement --no-undefined flag.

llvm-svn: 249064
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index f6a0629..7375b74 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -126,6 +126,7 @@
   Config->DiscardNone = Args.hasArg(OPT_discard_none);
   Config->ExportDynamic = Args.hasArg(OPT_export_dynamic);
   Config->NoInhibitExec = Args.hasArg(OPT_noinhibit_exec);
+  Config->NoUndefined = Args.hasArg(OPT_no_undefined);
   Config->Shared = Args.hasArg(OPT_shared);
 
   for (auto *Arg : Args) {