[clang] [clang][InstallAPI] Introduce basic driver to write out tbd files (PR #81571)

[Juergen Ributzka via cfe-commits]

================
@@ -4319,6 +4324,12 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
     if (!MergerInputs.empty())
       Actions.push_back(
           C.MakeAction<IfsMergeJobAction>(MergerInputs, types::TY_Image));
+  } else if (Args.hasArg(options::OPT_installapi)) {
+    assert(Inputs.size() == 1 && "InstallAPI action can only handle 1 input");
----------------
ributzka wrote:

Could you please add a comment or TODO?

https://github.com/llvm/llvm-project/pull/81571