[llvm] [llvm][utils] Avoid 'raw_string_ostream::str()' (NFC) (PR #97160)

[Youngsuk Kim via llvm-commits]

JOE1994 wrote:

Below is the TODO comment I'm referring to:

https://github.com/llvm/llvm-project/blob/804415825b97e974c96a92580bcbeaf4c7ff0a04/llvm/include/llvm/Support/raw_ostream.h#L676-L679

https://github.com/llvm/llvm-project/pull/97160