[llvm] [GOFF] Refactor GOFFOstream (PR #131143)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay approved this pull request.

Thanks!  I am not familiar with GOFF, but the code is much cleaner. Inheriting from raw_ostream from a target file was quite unusual.

https://github.com/llvm/llvm-project/pull/131143