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

[David Tenty via llvm-commits]

daltenty wrote:

@madanial0 was working for an alternative fix for this as part of: 
https://github.com/llvm/llvm-project/pull/199096/changes#diff-3aafd971924095743946ae0f1cc70b168d92cc8f49e5dd52458d9d4e1d3d87c6R2489

Namely, that was changing the default for llvm-nm to be `-Xany`. I think I'd rather split out and adopt that change, as it fixes the problem more broadly, rather than applying a lit config fix.

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