[libunwind] [libunwind] Remove unnecessary dependencies on fprintf and stdio.h for increased baremetal friendliness (PR #72040)

[Michael Kenzel via cfe-commits]

michael-kenzel wrote:

@arichardson as promised, I have rebased the changes. I'm not sure about the test failures, it would seem to me that they are unlikely to be caused by anything I did?

https://github.com/llvm/llvm-project/pull/72040