[libunwind] [libunwind] Use consistent indentation in `__libunwind_config.h` (PR #152861)

[Nikolas Klauser via cfe-commits]

https://github.com/philnik777 commented:

Should we maybe just set `IndentPPDirectives: AfterHash`? We already do that in libc++, libc++abi and (I think) compiler-rt.

https://github.com/llvm/llvm-project/pull/152861