[llvm] [doc] Add missing info for multiply specifiable objcopy opts (PR #111153)

[Fangrui Song via llvm-commits]

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@@ -120,7 +120,8 @@ multiple file formats.
 .. option:: --remove-symbol-prefix <prefix>
 
  Remove ``<prefix>`` from the start of every symbol name. No-op for symbols that do
- not start with ``<prefix>``.
+ not start with ``<prefix>``. Can be specified multiple times to remove multiple
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MaskRay wrote:

I am thinking of some variants, e.g.

"The option can be specified more than once." Each candidate can use exactly the same message.

"Multiple occurrences are feasible."

https://github.com/llvm/llvm-project/pull/111153