[llvm] enable file-headers option of llvm-objdump for XCOFF object files (PR #96104)

[James Henderson via llvm-commits]

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+# Test the `--file-headers` option of llvm-objdump for XCOFF object files.  
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jh7370 wrote:

Nit: newer tools tests use `##` for comments, to distinguish from lit directives like `RUN:`

https://github.com/llvm/llvm-project/pull/96104