[llvm] [llvm-objdump] Add triple support to `mcpu=help` (PR #165661)

[James Henderson via llvm-commits]

================
@@ -3533,6 +3533,19 @@ commaSeparatedValues(const llvm::opt::InputArgList &InputArgs, int ID) {
   return Values;
 }
 
+static void mcpuHelp() {
+  if (!TripleName.empty()) {
+    std::string Error;
+    Triple DummyTriple(TripleName);
+    const Target *DummyTarget =
+        TargetRegistry::lookupTarget(DummyTriple, Error);
+    if (!DummyTarget)
+      reportCmdLineError(Error);
+    // createMCSubtargetInfo prints the mcpu help text when called with "help"
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jh7370 wrote:

```suggestion
    // createMCSubtargetInfo prints the mcpu help text when called with "help".
```

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