[llvm] [yaml2obj][MachO] Fix crash from integer underflow with invalid cmdsize (PR #165924)

[James Henderson via llvm-commits]

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+## Test that yaml2obj handles cmdsize that is too small for LC_SEGMENT_64
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jh7370 wrote:

The fact that this uses a segment type is actually largely irrelevant to the behaviour under test, so I'd replace "segment" in the test name with "load-command" or similar.

Similar comment applies to this comment.

https://github.com/llvm/llvm-project/pull/165924