[llvm] [flang][AIX] Set OBJECT_MODE=any for invoking llvm-nm in LIT test (NFC) (PR #203400)

[Michael Kruse via llvm-commits]

https://github.com/Meinersbur commented:

Maybe add OBJECT_MODE=any to the environment variable instead so they apply to all commands? Or is there a reason it should only apply to llvm-nm invoked by a RUN: line?

https://github.com/llvm/llvm-project/pull/203400