[llvm] [readtapi] Add Merge functionality (PR #72656)

[Juergen Ributzka via llvm-commits]

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@@ -138,8 +155,22 @@ int main(int Argc, char **Argv) {
     }
   }
 
+  if (Args.hasArg(OPT_compact))
+    Ctx.Compact = true;
+
+  if (opt::Arg *A = Args.getLastArg(OPT_filetype_EQ)) {
+    Ctx.WriteFT = TextAPIWriter::parseFileType(A->getValue());
+    if (Ctx.WriteFT < FileType::TBD_V3 || Ctx.WriteFT == FileType::Invalid) {
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ributzka wrote:

I wonder if separate error messages should be returned here. One that says that `tbd-v1` and `tbd-v2` are deprecated and are no longer supported. And another error message if an unknown file type has been provided.

https://github.com/llvm/llvm-project/pull/72656