[llvm] [XCOFF][OBJECT] get symbol size by calling XCOFF interfaces (PR #67304)

[James Henderson via llvm-commits]

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jh7370 wrote:

Nit: please add comments explaining the purpose of this test.

This test is called "xcoff.test", implying it's supposed to be about generic xcoff functionality, but the patch is specifically about symbol sizes. Can the test be more focused?

https://github.com/llvm/llvm-project/pull/67304