[llvm] [llvm-nm] Introduce synthetic flag (PR #138232)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

Unfortunately, it's likely to be a few weeks before I can take a look at this. In the meantime, please add the option to the command guide (llvm/docs/CommandGuide/llvm-nm.rst). Please also see if the pre-merge failures are anything to do with your change.

https://github.com/llvm/llvm-project/pull/138232