[llvm] [CommandLine][NFCI] Simplify enumerating subcommands of an option (PR #75679)

[Nikita Popov via llvm-commits]

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@@ -175,6 +175,24 @@ class CommandLineParser {
                                StringRef Overview, raw_ostream *Errs = nullptr,
                                bool LongOptionsUseDoubleDash = false);
 
+  void forEachSubCommand(Option &Opt,
+                         std::function<void(SubCommand &)> Action) {
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nikic wrote:

Please use function_ref instead of std::function here.

https://github.com/llvm/llvm-project/pull/75679