[docs] Fix duplicate arguments for JoinedAndSeparate

[Hahnfeld]

Summary

We can't see how many arguments are in the meta var name, so just
assume that is the right number.

[Hahnfeld]

Ping

[aaron.ballman]

This LGTM, but you should wait a few days in case Richard has thoughts or concerns.

utils/TableGen/ClangOptionDocEmitter.cpp

for (auto Arg : Args) {
     OS << Separator << escapeRST(Arg);
     Separator = Separators.second;
   }
 }
 
 void emitOptionName(StringRef Prefix, const Record *Option, raw_ostream &OS) {
   // Find the arguments to list after the option.
   unsigned NumArgs = getNumArgsForKind(Option->getValueAsDef("Kind"), Option);
+  bool HasMetaVarName = !Option->isValueUnset("MetaVarName");
 
   std::vector<std::string> Args;
-  if (!Option->isValueUnset("MetaVarName"))
+  if (HasMetaVarName)
     Args.push_back(Option->getValueAsString("MetaVarName"));
   else if (NumArgs == 1)
     Args.push_back("<arg>");
 
+  // Fill up arguments if this option didn't provide a meta var name or it
+  // supports an unlimited number of arguments. We can't see how many arguments
+  // already are in a meta var name, so assume it has right number. This is
+  // needed for JoinedAndSeparate options so that there arent't too many
+  // arguments.
+  if (!HasMetaVarName || NumArgs == UnlimitedArgs) {
     while (Args.size() < NumArgs) {
       Args.push_back(("<arg" + Twine(Args.size() + 1) + ">").str());
       // Use '--args <arg1> <arg2>...' if any number of args are allowed.
       if (Args.size() == 2 && NumArgs == UnlimitedArgs) {
         Args.back() += "...";
         break;
       }
     }
+  }
 
   emitOptionWithArgs(Prefix, Option, std::vector<StringRef>(Args.begin(), Args.end()), OS);
 
   auto AliasArgs = Option->getValueAsListOfStrings("AliasArgs");
   if (!AliasArgs.empty()) {
     Record *Alias = Option->getValueAsDef("Alias");
     OS << " (equivalent to ";
     emitOptionWithArgs(