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

[Cyndy Ishida via cfe-commits]

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@@ -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");
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cyndyishida wrote:

This is temporary and will be lifted when we can handle multiple inputs. Worth noting though, that I'm going to keep the original `tapi` input style where we only accept directory structures or JSON input. 

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