[clang] [DebugInfo] Add flag to only emit referenced member functions (PR #87018)

[Stephen Tozer via cfe-commits]

================
@@ -4260,6 +4260,13 @@ defm strict_dwarf : BoolOption<"g", "strict-dwarf",
           "the specified version, avoiding features from later versions.">,
   NegFlag<SetFalse>, BothFlags<[], [ClangOption, CLOption, DXCOption]>>,
   Group<g_flags_Group>;
+defm omit_unreferenced_members : BoolOption<"g", "omit-unreferenced-members",
+  CodeGenOpts<"DebugOmitUnreferencedMembers">, DefaultFalse,
+  PosFlag<SetTrue, [], [ClangOption, CC1Option],
+  	"Omit member function declarations from type descriptions if the "
+	"member is unreferenced.">,
+  NegFlag<SetFalse>, BothFlags<[], [ClangOption, CLOption, DXCOption]>>,
+  Group<g_flags_Group>;
----------------
SLTozer wrote:

As a small matter of convenience, since this is just being passed straight through the driver I think this could be a marshalling flag, which iirc would allow us to omit the `renderDebugOptions` code?
```suggestion
defm omit_unreferenced_members : Flag<["-"], "gomit-unreferenced-members">,
  Group<g_flags_Group>, Visibility<[ClangOption, CC1Option]>,
  HelpText<"Omit member function declarations from type descriptions if the "
	"member is unreferenced.">,
  MarshallingInfoFlag<CodeGenOpts<"DebugOmitUnreferencedMembers">>;
```

https://github.com/llvm/llvm-project/pull/87018