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

[James Henderson via llvm-commits]

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@@ -200,6 +200,9 @@ Changes to the LLVM tools
   emitted on stdout, to account for spaces or other special characters in path.
   (`#97305 <https://github.com/llvm/llvm-project/pull/97305>`_).
 
+* `llvm-objdump` now supports using `--mcpu=help` with the `--triple` option
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jh7370 wrote:

Needs updating to mention `--mattr=help` too.

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