[llvm] [llvm-objdump] Support --mcpu=help/--mattr=help without -d (PR #165661)

[Ruoyu Qiu via llvm-commits]

================
@@ -3533,6 +3533,33 @@ commaSeparatedValues(const llvm::opt::InputArgList &InputArgs, int ID) {
   return Values;
 }
 
+static void mcpuHelp() {
+  std::string Error;
+  Triple TheTriple;
+
+  if (!TripleName.empty()) {
+    TheTriple.setTriple(TripleName);
+  } else {
+    // We can guarantee that InputFilenames won't be empty.
+    Expected<OwningBinary<Binary>> OBinary = createBinary(InputFilenames[0]);
+    // OwningBinary<Binary> OBinary =
+    if (!OBinary)
+      reportError(InputFilenames[0],
+                  "A target triple was not specified and could "
+                  " not be inferred from the input file.");
+
+    Binary *Bin = OBinary->getBinary();
+    if (ObjectFile *Obj = dyn_cast<ObjectFile>(Bin))
----------------
cabbaken wrote:

Would it be acceptable to simply emit an error for now?
```cpp
    if (ObjectFile *Obj = dyn_cast<ObjectFile>(Bin))
      TheTriple = Obj->makeTriple();
    else
      reportError(InputFilenames[0], "file type unrecognized, please input an object file");
```
Does this error message look appropriate?

https://github.com/llvm/llvm-project/pull/165661