[llvm][support] show name of overlapping cl opt

Author: makslevental

llvm/include/llvm/Support/CommandLine.h

@@ -863,7 +863,10 @@ template <class DataType> class parser : public generic_parser_base {
   ///
   template <class DT>
   void addLiteralOption(StringRef Name, const DT &V, StringRef HelpStr) {
-    assert(findOption(Name) == Values.size() && "Option already exists!");
+#ifndef NDEBUG
+    if (findOption(Name) != Values.size())
+      report_fatal_error("Option " + Name + " already exists!");
+#endif
     OptionInfo X(Name, static_cast<DataType>(V), HelpStr);
     Values.push_back(X);
     AddLiteralOption(Owner, Name);