[Bash-autocompletion] Show flags which has HelpText or GroupID

[yamaguchi]

Summary

Otherwise internal flags will be also completed.

[teemperor]

For the record, one can get a (maybe incomplete) list of options that are without completion via: curl "https://teemperor.de/pub/clang_flags.txt" | grep -v HelpText | grep -v Group.
The only options I can see that I would miss if they would disappear are the ones who are clearly meant to be public but just lack the HelpText (like our beloved sysroot, which is a public GCC flag). So I think this patch can go forward and someone will have to add a HelpText for those flags in the future.

[yamaguchi]

We are going to ask community which flags should be autocompleted or not, and tidy Options.td.

llvm/trunk/lib/Option/OptTable.cpp

for (const Info &In : OptionInfos.slice(FirstSearchableIndex)) {
     return Result;
   }
   return {};
 }
 
 std::vector<std::string> OptTable::findByPrefix(StringRef Cur) const {
   std::vector<std::string> Ret;
   for (const Info &In : OptionInfos.slice(FirstSearchableIndex)) {
-    if (!In.Prefixes)
+    if (!In.Prefixes || (!In.HelpText && !In.GroupID))
       continue;
     for (int I = 0; In.Prefixes[I]; I++) {
       std::string S = std::string(In.Prefixes[I]) + std::string(In.Name);
       if (StringRef(S).startswith(Cur))
         Ret.push_back(S);
     }
   }
   return Ret;